Liquid crystal mixture and liquid crystal display

ABSTRACT

The invention relates to a compound of formula I,wherein R11, R21, A11, A, Z, X11, X21, Y11, Y12, Sp11, Sp21, o and p have one of the meanings as given in claim 1. The invention further relates to method of production of a compound of formula I, to the use of said compounds in LC media and to LC media comprising one or more compounds of formula I. Further, the invention relates to a method of production of such LC media, to the use of such media in LC devices, and to LC device comprising a LC medium according to the present invention. The present invention further relates to a process for the fabrication such liquid crystal display and to the use of the liquid crystal mixtures according to the invention for the fabrication of such liquid crystal display.

The invention relates to compounds of formula I,

wherein R¹¹, R²¹, A¹¹, A, Z, X¹¹, X²¹, Y¹¹, Y¹², Sp¹¹, Sp²¹, o and phave one of the meanings as given in claim 1. The invention furtherrelates to a method of production of said compounds, to the use of saidcompounds in LC media and to LC media comprising one or more compoundsof formula I. Further, the invention relates to a method of productionof such LC media, to the use of such media in LC devices, and to a LCdevice comprising a LC medium according to the present invention. Thepresent invention further relates to a process for the fabrication suchliquid crystal display and to the use of the liquid crystal mixturesaccording to the invention for the fabrication of such liquid crystaldisplay.

BACKGROUND AND PRIOR ART

Liquid-crystalline media have been used for decades in electro-opticaldisplays for information display. The liquid crystal displays used atpresent are usually those of the TN (“twisted nematic”) type. However,these have the disadvantage of a strong viewing-angle dependence of thecontrast.

In addition, so-called VA (“vertically aligned”) displays are knownwhich have a broader viewing angle. The LC cell of a VA display containsa layer of an LC medium between two transparent electrodes, where the LCmedium usually has a negative value of the dielectric (DC) anisotropy.In the switched-off state, the molecules of the LC layer are alignedperpendicular to the electrode surfaces (homeotropically) or have atilted homeotropic alignment. On application of an electrical voltage tothe two electrodes, a realignment of the LC molecules parallel to theelectrode surfaces takes place. Furthermore, so-called IPS (“in planeswitching”) displays and later, FFS (“fringe-field switching”) displayshave been reported (see, inter alia, S. H. Jung et al., Jpn. J. Appl.Phys., Volume 43, No. 3, 2004, 1028), which contain two electrodes onthe same substrate, one of which is structured in a comb-shaped mannerand the other is unstructured. A strong, so-called “fringe field” isthereby generated, i.e. a strong electric field close to the edge of theelectrodes, and, throughout the cell, an electric field which has both astrong vertical component and a strong horizontal component. FFSdisplays have a low viewing-angle dependence of the contrast. FFSdisplays usually contain an LC medium with positive dielectricanisotropy, and an alignment layer, usually of polyimide, which providesplanar alignment to the molecules of the LC medium.

Furthermore, FFS displays have been disclosed (see S. H. Lee et al.,Appl. Phys. Lett. 73(20), 1998, 2882-2883 and S. H. Lee et al., LiquidCrystals 39(9), 2012, 1141-1148), which have similar electrode designand layer thickness as FFS displays, but comprise a layer of an LCmedium with negative dielectric anisotropy instead of an LC medium withpositive dielectric anisotropy. The LC medium with negative dielectricanisotropy shows a more favorable director orientation that has lesstilt and more twist orientation compared to the LC medium with positivedielectric anisotropy, as a result of which these displays have a highertransmission.

A further development are the so-called PS (polymer sustained) or PSA(polymer sustained alignment) displays, for which the term “polymerstabilised” is also occasionally used. The PSA displays aredistinguished by the shortening of the response times withoutsignificant adverse effects on other parameters, such as, in particular,the favourable viewing-angle dependence of the contrast.

In these displays, a small amount (for example 0.3% by weight, typically<1% by weight) of one or more polymerizable compound(s) is added to theLC medium and, after introduction into the LC cell, is polymerised orcrosslinked in situ, usually by UV photopolymerization, between theelectrodes with or without an applied electrical voltage. The additionof polymerizable mesogenic or liquid-crystalline compounds, also knownas reactive mesogens or “RMs”, to the LC mixture has proven particularlysuitable. PSA technology has hitherto been employed principally for LCmedia having negative dielectric anisotropy.

Unless indicated otherwise, the term “PSA” is used below asrepresentative of PS displays and PSA displays.

In the meantime, the PSA principle is being used in diverse classical LCdisplays. Thus, for example, PSA-VA, PSA-OCB, PSA-IPS, PSA-FFS andPSA-TN displays are known. The polymerisation of the polymerizablecompound(s) preferably takes place with an applied electrical voltage inthe case of PSA-VA and PSA-OCB displays, and with or without an appliedelectrical voltage in the case of PSA-IPS displays. As can bedemonstrated in test cells, the PS(A) method results in a ‘pretilt’ inthe cell. In the case of PSA-OCB displays, for example, it is possiblefor the bend structure to be stabilised so that an offset voltage isunnecessary or can be reduced. In the case of PSA-VA displays, thepretilt has a positive effect on the response times. A standard MVA orPVA pixel and electrode layout can be used for PSA-VA displays. Inaddition, however, it is also possible, for example, to manage with onlyone structured electrode side and no protrusions, which significantlysimplifies production and at the same time results in very good contrastat the same time as very good light transmission.

PSA-VA displays are described, for example, in JP 10-036847 A, EP 1 170626 A2, U.S. Pat. Nos. 6,861,107, 7,169,449, US 2004/0191428 A1, US2006/0066793 A1 and US 2006/0103804 A1. PSA-OCB displays are described,for example, in T.-J-Chen et al., Jpn. J. Appl. Phys. 45, 2006,2702-2704 and S. H. Kim, L.-C-Chien, Jpn. J. Appl. Phys. 43, 2004,7643-7647. PSA-IPS displays are described, for example, in U.S. Pat. No.6,177,972 and Appl. Phys. Lett. 1999, 75(21), 3264. PSA-TN displays aredescribed, for example, in Optics Express 2004, 12(7), 1221. PSAVA-IPSdisplays are disclosed, for example, in WO 2010/089092 A1.

Like the conventional LC displays described above, PSA displays can beoperated as active-matrix or passive-matrix displays. In the case ofactive-matrix displays, individual pixels are usually addressed byintegrated, non-linear active elements, such as, for example,transistors (for example thin-film transistors or “TFTs”), while in thecase of passive-matrix displays, individual pixels are usually addressedby the multiplex method, both methods being known from the prior art.

In the prior art, polymerizable compounds of the following formula, forexample, are used for PSA-VA:

in which P denotes a polymerizable group, usually an acrylate ormethacrylate group, as described, for example, in U.S. Pat. No.7,169,449.

Below the polymer layer which induces the above mentioned pretilt, anorientation layer—usually a polyimide—provides the initial alignment ofthe liquid crystal regardless of the polymer stabilisation step of theproduction process.

The effort for the production of a polyimide layer, treatment of thelayer and improvement with bumps or polymer layers is relatively great.A simplifying technology which on the one hand reduces production costsand on the other hand helps to optimise the image quality (viewing-angledependence, contrast, response times) would therefore be desirable.Rubbed polyimide has been used for a long time to align liquid crystals.The rubbing process causes a number of problems: mura, contamination,problems with static discharge, debris, etc.

Photoalignment is a technology for achieving liquid crystal (LC)alignment that avoids rubbing by replacing it with a light-inducedorientational ordering of the alignment surface. This can be achievedthrough the mechanisms of photodecomposition, photodimerization, andphotoisomerization (N. A. Clark et al. Langmuir 2010, 26(22),17482-17488, and literature cited therein) by means of polarised light.However, still a suitably derivatised polyimide layer is required thatcomprises the photoreactive group. A further improvement would be toavoid the use of polyimide at all. For VA displays this was achieved byadding a self-alignment agent to the LC that induces homeotropicalignment in situ by a self-assembling mechanism as disclosed in WO2012/104008 and WO 2012/038026.

N. A. Clark et al. Langmuir 2010, 26(22), 17482-17488 have shown that itis possible to self-assemble a compound of the following structure

onto a substrate to give a monolayer that is able to be photoaligned toinduce homogeneous alignment of a liquid crystal. However, a separatestep of self-assembly before manufacture of the LC cell is required andthe nature of the azo-group causes reversibility of the alignment whenexposed to light.

Another functional group known to enable photoalignment is thephenylethenylcarbonyloxy group (cinnamate). Photocrosslinkablecinnamates are known from the prior art, e.g. of the following structure

as disclosed in EP0763552. From such compounds, polymers can beobtained, for example the following

This material was used in a photoalignment process, as disclosed in WO99/49360, to give an orientation layer for liquid crystals. Adisadvantage of orientation layers obtained by this process is that theygive lower voltage holding ratios (VHR) than polyimides.

In WO 00/05189 polymerizable direactive mesogenic cinnamates aredisclosed for the use in polymerizable LC mixtures for e.g. opticalretarders.

A structurally related compound of the following formula

comprising two cinnamic acid moieties is disclosed in GB 2 306 470 A forthe use as component in liquid crystalline polymer films. This type ofcompound has not been used or proposed for the use as photoalignmentagent.

A very similar compound is published in B.M.I. van der Zande et al.,Liquid Crystals, Vol. 33, No. 6, June 2006, 723-737, in the field ofliquid crystalline polymers for patterned retarders, and has thefollowing structure:

WO 2017/102068 A1 discloses the same structure for the purpose of apolyimide-free homogeneous photoalignment method.

Further, M. H. Lee et al. published in Liquid Crystals(https://doi.org/10.1080/02678292.2018.1441459) a polyimide-freehomogeneous photoalignment method induced by polymerizable liquidcrystal containing cinnamate moiety of the following formula:

Thus, there is a great demand for new photoreactive mesogens that enablephotoalignment of a liquid crystal mixture in situ, i.e. after assemblyof the display, by means of linearly polarized light.

In addition to this requirement, the corresponding photoreactive mesogenshould provide, preferably at the same time, a liquid crystal displayhaving favourable high dark state and a favourable high voltage holdingratio. Furthermore, the amount of photoreactive mesogens in the nematicLC medium should be a low as possible and the process for the productionshould be obtainable from a process that is compatible with common massproduction processes, e.g. in terms of favourable short processingtimes.

Other aims of the present invention are immediately evident to theperson skilled in the art from the following detailed description.

Surprisingly, the inventors have found out that one or more of theabove-mentioned aims can be achieved by providing a compound accordingto claim 1.

Terms and Definitions

A photoreactive group according to the present invention is a functionalgroup of a molecule that causes a change of the geometry of the moleculeeither by bond rotation, skeletal rearrangement or atom- orgroup-transfer, or by dimerization, upon irradiation with light of asuitable wavelength that can be absorbed by the molecule.

The term “mesogenic group” as used herein is known to the person skilledin the art and described in the literature, and means a group which, dueto the anisotropy of its attracting and repelling interactions,essentially contributes to causing a liquid-crystal (LC) phase inlow-molecular-weight or polymeric substances. Compounds containingmesogenic groups (mesogenic compounds) do not necessarily have to havean LC phase themselves. It is also possible for mesogenic compounds toexhibit LC phase behaviour only after mixing with other compounds and/orafter polymerisation. Typical mesogenic groups are, for example, rigidrod- or disc-shaped units. An overview of the terms and definitions usedin connection with mesogenic or LC compounds is given in Pure Appl.Chem. 2001, 73(5), 888 and C. Tschierske, G. Pelzl, S. Diele, Angew.Chem. 2004, 116, 6340-6368.

A photoreactive mesogen according to the present invention is amesogenic compound comprising one or more photoreactive groups.

Examples of photoreactive groups are —C═C— double bonds and azo groups(—N═N—).

Examples of molecular structures and sub-structures comprising suchphotoreactive groups are stilbene,(1,2-difluoro-2-phenyl-vinyl)-benzene, cinnamate,4-phenylbut-3-en-2-one, chalcone, coumarin, chromone, pentalenone andazobenzene.

According to the present application, the term “linearly polarisedlight” means light, which is at least partially linearly polarized.Preferably, the aligning light is linearly polarized with a degree ofpolarization of more than 5:1. Wavelengths, intensity and energy of thelinearly polarised light are chosen depending on the photosensitivity ofthe photoalignable material. Typically, the wavelengths are in the UV-A,UV-B and/or UV-C range or in the visible range. Preferably, the linearlypolarised light comprises light of wavelengths less than 450 nm, morepreferably less than 420 nm at the same time the linearly polarisedlight preferably comprises light of wavelengths longer than 280 nm,preferably more than 320 nm, more preferably over 350 nm.

The term “organic group” denotes a carbon or hydrocarbon group.

The term “carbon group” denotes a mono- or polyvalent organic groupcontaining at least one carbon atom, where this either contains nofurther atoms (such as, for example, —C≡C—) or optionally contains oneor more further atoms, such as, for example, N, O, S, P, Si, Se, As, Teor Ge (for example carbonyl, etc.). The term “hydrocarbon group” denotesa carbon group which additionally contains one or more H atoms andoptionally one or more heteroatoms, such as, for example, N, O, S, P,Si, Se, As, Te or Ge.

“Halogen” denotes F, Cl, Br or I.

A carbon or hydrocarbon group can be a saturated or unsaturated group.Unsaturated groups are, for example, aryl, alkenyl or alkynyl groups. Acarbon or hydrocarbon radical having 3 or more atoms can bestraight-chain, branched and/or cyclic and may also contain spiro linksor condensed rings.

The terms “alkyl”, “aryl”, “heteroaryl”, etc., also encompass polyvalentgroups, for example alkylene, arylene, heteroarylene, etc.

The term “aryl” denotes an aromatic carbon group or a group derivedtherefrom. The term “heteroaryl” denotes “aryl” as defined above,containing one or more heteroatoms.

Preferred carbon and hydrocarbon groups are optionally substitutedalkyl, alkenyl, alkynyl, alkoxy, alkylcarbonyl, alkoxycarbonyl,alkylcarbonyloxy and alkoxycarbonyloxy having 1 to 40, preferably 1 to25, particularly preferably 1 to 18, C atoms, optionally substitutedaryl or aryloxy having 6 to 40, preferably 6 to 25, C atoms, oroptionally substituted alkylaryl, arylalkyl, alkylaryloxy, arylalkyloxy,arylcarbonyl, aryloxycarbonyl, arylcarbonyloxy and aryloxycarbonyloxyhaving 6 to 40, preferably 6 to 25, C atoms.

Further preferred carbon and hydrocarbon groups are C₁-C₄₀ alkyl, C₂-C₄₀alkenyl, C₂-C₄₀ alkynyl, C₃-C₄₀ allyl, C₄-C₄₀ alkyldienyl, C₄-C₄₀polyenyl, C₆-C₄₀ aryl, C₆-C₄₀ alkylaryl, C₆-C₄₀ arylalkyl, C₆-C₄₀alkylaryloxy, C₆-C₄₀ arylalkyloxy, C₂-C₄₀ heteroaryl, C₄-C₄₀ cycloalkyl,C₄-C₄₀ cycloalkenyl, etc. Particular preference is given to C₁-C₂₂alkyl, C₂-C₂₂ alkenyl, C₂-C₂₂ alkynyl, C₃-C₂₂ allyl, C₄-C₂₂ alkyldienyl,C₆-C₁₂ aryl, C₆-C₂₀ arylalkyl and C₂-C₂₀ heteroaryl.

Further preferred carbon and hydrocarbon groups are straight-chain,branched or cyclic alkyl radicals having 1 to 40, preferably 1 to 25, Catoms, which are unsubstituted or mono- or polysubstituted by F, Cl, Br,I or CN and in which one more non-adjacent CH₂ groups may each bereplaced, independently of one another, by —C(R^(z))═C(R^(z))—, —C≡C—,—N(R^(z))—, —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O— in such a way that0 and/or S atoms are not linked directly to one another.

R^(z) preferably denotes H, halogen, a straight-chain, branched orcyclic alkyl chain having 1 to 25 C atoms, in which, in addition, one ormore non-adjacent C atoms may be replaced by —O—, —S—, —CO—, —CO—O—,—O—CO— or —O—CO—O— and in which one or more H atoms may be replaced byfluorine, an optionally substituted aryl or aryloxy group having 6 to 40C atoms, or an optionally substituted heteroaryl or heteroaryloxy grouphaving 2 to 40 C atoms.

Preferred alkyl groups are, for example, methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, 2-methylbutyl, n-pentyl,s-pentyl, cyclopentyl, n-hexyl, cyclohexyl, 2-ethylhexyl, n-heptyl,cycloheptyl, n-octyl, cyclooctyl, n-nonyl, n-decyl, n-undecyl,n-dodecyl, trifluoromethyl, perfluoro-n-butyl, 2,2,2-trifluoroethyl,perfluorooctyl and perfluorohexyl.

Preferred alkenyl groups are, for example, ethenyl, propenyl, butenyl,pentenyl, cyclopentenyl, hexenyl, cyclohexenyl, heptenyl, cycloheptenyl,octenyl and cyclooctenyl.

Preferred alkynyl groups are, for example, ethynyl, propynyl, butynyl,pentynyl, hexynyl and octynyl.

Preferred alkoxy groups are, for example, methoxy, ethoxy,2-methoxyethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy, s-butoxy,t-butoxy, 2-methylbutoxy, n-pentoxy, n-hexoxy, n-heptoxy, n-octoxy,n-nonoxy, n-decoxy, n-undecoxy and n-dodecoxy.

Preferred amino groups are, for example, dimethylamino, methylamino,methylphenylamino and phenylamino.

Aryl and heteroaryl groups can be monocyclic or polycyclic, i.e. theycan contain one ring (such as, for example, phenyl) or two or morerings, which may also be fused (such as, for example, naphthyl) orcovalently bonded (such as, for example, biphenyl), or contain acombination of fused and linked rings. Heteroaryl groups contain one ormore heteroatoms, preferably selected from O, N, S and Se. A ring systemof this type may also contain individual non-conjugated units, as is thecase, for example, in the fluorene basic structure.

Particular preference is given to mono-, bi- or tricyclic aryl groupshaving 6 to 25 C atoms and mono-, bi- or tricyclic heteroaryl groupshaving 2 to 25 C atoms, which optionally contain fused rings and areoptionally substituted. Preference is furthermore given to 5-, 6- or7-membered aryl and heteroaryl groups, in which, in addition, one ormore CH groups may be replaced by N, S or O in such a way that O atomsand/or S atoms are not linked directly to one another.

Preferred aryl groups are derived, for example, from the parentstructures benzene, biphenyl, terphenyl, [1,1′:3′,1″]terphenyl,naphthalene, anthracene, binaphthyl, phenanthrene, pyrene,dihydropyrene, chrysene, perylene, tetracene, pentacene, benzopyrene,fluorene, indene, indenofluorene, spirobifluorene, etc.

Preferred heteroaryl groups are, for example, 5-membered rings, such aspyrrole, pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, tetrazole,furan, thiophene, selenophene, oxazole, isoxazole, 1,2-thiazole,1,3-thiazole, 1,2,3-oxadiazole, 1,2,4-oxadiazole, 1,2,5-oxadiazole,1,3,4-oxadiazole, 1,2,3-thiadiazole, 1,2,4-thiadiazole,1,2,5-thiadiazole, 1,3,4-thiadiazole, 6-membered rings, such aspyridine, pyridazine, pyrimidine, pyrazine, 1,3,5-triazine,1,2,4-triazine, 1,2,3-triazine, 1,2,4,5-tetrazine, 1,2,3,4-tetrazine,1,2,3,5-tetrazine, or condensed groups, such as indole, isoindole,indolizine, indazole, benzimidazole, benzotriazole, purine,naphthimidazole, phenanthrimidazole, pyridimidazole, pyrazinimidazole,quinoxalinimidazole, benzoxazole, naphthoxazole, anthroxazole,phenanthroxazole, isoxazole, benzothiazole, benzofuran, isobenzofuran,dibenzofuran, quinoline, isoquinoline, pteridine, benzo-5,6-quinoline,benzo-6,7-quinoline, benzo-7,8-quinoline, benzoisoquinoline, acridine,phenothiazine, phenoxazine, benzopyridazine, benzopyrimidine,quinoxaline, phenazine, naphthyridine, azacarbazole, benzocarboline,phenanthridine, phenanthroline, thieno[2,3b]thiophene,thieno[3,2b]thiophene, dithienothiophene, dihydrothieno[3,4-b]-1,4-dioxin, isobenzothiophene, dibenzothiophene,benzothiadiazothiophene, or combinations of these groups. The heteroarylgroups may also be substituted by alkyl, alkoxy, thioalkyl, fluorine,fluoroalkyl or further aryl or heteroaryl groups.

The (non-aromatic) alicyclic and heterocyclic groups encompass bothsaturated rings, i.e. those containing exclusively single bonds, andalso partially unsaturated rings, i.e. those which may also containmultiple bonds. Heterocyclic rings contain one or more heteroatoms,preferably selected from Si, O, N, S and Se.

The (non-aromatic) alicyclic and heterocyclic groups can be monocyclic,i.e. contain only one ring (such as, for example, cyclohexane), orpolycyclic, i.e. contain a plurality of rings (such as, for example,decahydronaphthalene or bicyclooctane). Particular preference is givento saturated groups. Preference is furthermore given to mono-, bi- ortricyclic groups having 3 to 25 C atoms, which optionally contain fusedrings and are optionally substituted. Preference is furthermore given to5-, 6-, 7- or 8-membered carbocyclic groups, in which, in addition, oneor more C atoms may be replaced by Si and/or one or more CH groups maybe replaced by N and/or one or more non-adjacent CH₂ groups may bereplaced by —O— and/or —S—.

Preferred alicyclic and heterocyclic groups are, for example, 5-memberedgroups, such as cyclopentane, tetrahydrofuran, tetrahydrothiofuran,pyrrolidine, 6-membered groups, such as cyclohexane, silinane,cyclohexene, tetrahydropyran, tetrahydrothiopyran, 1,3-dioxane,1,3-dithiane, piperidine, 7-membered groups, such as cycloheptane, andfused groups, such as tetrahydronaphthalene, decahydronaphthalene,indane, bicyclo[1.1.1]pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl,spiro[3.3]heptane-2,6-diyl, octahydro-4,7-methanoindane-2,5-diyl.

The aryl, heteroaryl, carbon and hydrocarbon radicals optionally haveone or more substituents, which are preferably selected from the groupcomprising silyl, sulfo, sulfonyl, formyl, amine, imine, nitrile,mercapto, nitro, halogen, C₁₋₁₂ alkyl, C₆₋₁₂ aryl, C₁₋₁₂ alkoxy,hydroxyl, or combinations of these groups.

Preferred substituents are, for example, solubility-promoting groups,such as alkyl or alkoxy, and electron-withdrawing groups, such asfluorine, nitro or nitrile.

Preferred substituents, unless stated otherwise, also referred to as “L”above and below, are F, Cl, Br, I, —CN, —NO₂, —NCO, —NCS, —OCN, —SCN,—C(═O)N(R^(z))₂, —C(═O)Y¹, —C(═O)R^(z), —N(R^(z))₂, in which R^(z) hasthe meaning indicated above, and Y¹ denotes halogen, optionallysubstituted silyl or aryl having 6 to 40, preferably 6 to 20, C atoms,and straight-chain or branched alkyl, alkoxy, alkylcarbonyl,alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 Catoms, preferably 2 to 12, in which one or more H atoms may optionallybe replaced by F or Cl.

“Substituted silyl or aryl” preferably means substituted by halogen,—CN, R^(y1), —OR^(y1), —CO—R^(y1), —CO—O—R^(y1), —O—CO—R^(y1) or—O—CO—O—R^(y1), in which R^(y1) has the meaning indicated above.

Particularly preferred substituents L are, for example, F, Cl, CN, CH₃,C₂H₅, —CH(CH₃)₂, OCH₃, OC₂H₅, CF₃, OCF₃, OCHF₂, OC₂F₅, furthermorephenyl.

Above and below “halogen” denotes F, Cl, Br or I.

Above and below, the terms “alkyl”, “aryl”, “heteroaryl”, etc., alsoencompass polyvalent groups, for example alkylene, arylene,heteroarylene, etc.

The term “director” is known in prior art and means the preferredorientation direction of the long molecular axes (in case of calamiticcompounds) or short molecular axes (in case of discotic compounds) ofthe liquid-crystalline molecules. In case of uniaxial ordering of suchanisotropic molecules, the director is the axis of anisotropy.

The term “alignment” or “orientation” relates to alignment (orientationordering) of anisotropic units of material such as small molecules orfragments of big molecules in a common direction named “alignmentdirection”. In an aligned layer of liquid-crystalline material, theliquid-crystalline director coincides with the alignment direction sothat the alignment direction corresponds to the direction of theanisotropy axis of the material.

The term “planar orientation/alignment”, for example in a layer of anliquid-crystalline material, means that the long molecular axes (in caseof calamitic compounds) or the short molecular axes (in case of discoticcompounds) of a proportion of the liquid-crystalline molecules areoriented substantially parallel (about 180°) to the plane of the layer.

The term “homeotropic orientation/alignment”, for example in a layer ofa liquid-crystalline material, means that the long molecular axes (incase of calamitic compounds) or the short molecular axes (in case ofdiscotic compounds) of a proportion of the liquid-crystalline moleculesare oriented at an angle θ (“tilt angle”) between about 80° to 90°relative to the plane of the layer.

The terms “uniform orientation” or “uniform alignment” of anliquid-crystalline material, for example in a layer of the material,mean that the long molecular axes (in case of calamitic compounds) orthe short molecular axes (in case of discotic compounds) of theliquid-crystalline molecules are oriented substantially in the samedirection. In other words, the lines of liquid-crystalline director areparallel.

The wavelength of light generally referred to in this application is 550nm, unless explicitly specified otherwise.

The birefringence Δn herein is defined by the following equationΔn=n _(e) −n _(o)wherein n_(e) is the extraordinary refractive index and no is theordinary refractive index and the effective average refractive index nayis given by the following equationn _(av.)=[(2n _(o) ² +n _(e) ²)/3]^(1/2)

The extraordinary refractive index n_(e) and the ordinary refractiveindex no can be measured using an Abbe refractometer.

In the present application the term “dielectrically positive” is usedfor compounds or components with Δε>3.0, “dielectrically neutral” with−1.5≤Δε≤3.0 and “dielectrically negative” with Δε<−1.5. Δε is determinedat a frequency of 1 kHz and at 20° C. The dielectric anisotropy of therespective compound is determined from the results of a solution of 10%of the respective individual compound in a nematic host mixture. In casethe solubility of the respective compound in the host medium is lessthan 10% its concentration is reduced by a factor of 2 until theresultant medium is stable enough at least to allow the determination ofits properties. Preferably, the concentration is kept at least at 5%,however, to keep the significance of the results as high as possible.The capacitance of the test mixtures are determined both in a cell withhomeotropic and with homogeneous alignment. The cell gap of both typesof cells is approximately 20 μm. The voltage applied is a rectangularwave with a frequency of 1 kHz and a root mean square value typically of0.5 V to 1.0 V; however, it is always selected to be below thecapacitive threshold of the respective test mixture.

Δε is defined as (ε∥−ε_(⊥)), whereas ε_(av). is (ε∥+2ε_(⊥))/3. Thedielectric permittivity of the compounds is determined from the changeof the respective values of a host medium upon addition of the compoundsof interest. The values are extrapolated to a concentration of thecompounds of interest of 100%. A typical host medium is ZLI-4792 orZLI-2857 both commercially available from Merck, Darmstadt.

For the present invention,

denote trans-1,4-cyclohexylene,

denote 1,4-phenylene.

For the present invention the groups —CO—O—, —COO— —C(═O)O— or —CO₂—denote an ester group of formula

and the groups —O—CO— —OCO—, —OC(═O)—, —O₂C— or —OOC— denote an estergroup of formula

Furthermore, the definitions as given in C. Tschierske, G. Pelzl and S.Diele, Angew. Chem. 2004, 116, 6340-6368 shall apply to non-definedterms related to liquid crystal materials in the instant application.

DETAILED DESCRIPTION

In detail, the present invention relates to photoreactive mesogens offormula I

wherein

-   A¹¹ denotes a radical

-   -   where, in addition, one or more H atoms in these radical may be        replaced by L, and/or one or more and/or one or more CH groups        may be replaced by N,

-   A denotes, independently of one another, in each occurrence    -   a) the group consisting of 1,4-phenylene and 1,3-phenylene,        wherein, in addition, one or two CH groups may be replaced by N        and wherein, in addition, one or more H atoms may be replaced by        L,    -   b) the group consisting of saturated, partially unsaturated or        fully unsaturated, and optionally substituted, polycyclic        radicals having 5 to 20 cyclic C atoms, one or more of which        may, in addition, be replaced by heteroatoms, preferably        selected from the group consisting of

-   -   where, in addition, one or more H atoms in these radicals may be        replaced by L, and/or one or more double bonds may be replaced        by single bonds, and/or one or more CH groups may be replaced by        N,    -   c) group consisting of trans-1,4-cyclohexylene,        1,4-cyclohexenylene, wherein, in addition, one or more        non-adjacent CH₂ groups may be replaced by —O— and/or —S— and        wherein, in addition, one or more H atoms may be replaced by F,        or    -   d) a group consisting of tetrahydropyran-2,5-diyl,        1,3-dioxane-2,5-diyl, tetrahydrofuran-2,5-diyl,        cyclobutane-1,3-diyl, piperidine-1,4-diyl, thiophene-2,5-diyl        and selenophene-2,5-diyl,    -   each of which may also be mono- or polysubstituted by L,

-   L on each occurrence, identically or differently, denotes —OH, —F,    —Cl, —Br, —I, —CN, —NO₂, SF₅, —NCO, —NCS, —OCN, —SCN,    —C(═O)N(R^(z))₂, —C(═O)R^(z), —N(R^(z))₂, optionally substituted    silyl, optionally substituted aryl having 6 to 20 C atoms, or    straight-chain or branched or cyclic alkyl, alkoxy, alkylcarbonyl,    alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25    C atoms, preferably 1 to 12 C atoms, more preferably 1 to 6 C atoms,    in which, in addition, one or more H atoms may be replaced by F or    Cl, or X²¹-Sp²¹-R²¹,

-   M denotes —O—, —S—, —CH₂—, —CHR^(z)— or —CR^(y)R^(z)—, and

-   R^(y) and R^(z) each, independently of one another, denote H, CN, F    or alkyl having 1-12 C atoms, wherein, in addition, one    -   or more H atoms may be replaced by F,    -   preferably H, methyl, ethyl, propyl, butyl,    -   more preferably H or methyl,    -   in particular H,

-   Y¹¹ and Y¹² each, independently of one another, denote H, F, phenyl    or optionally fluorinated alkyl having 1-12 C atoms, preferably H,    methyl, ethyl, propyl, butyl, more preferably H or methyl,    -   in particular H,

-   Z denotes, independently of each other, in each occurrence, a single    bond, —OOC—, —OCO—, —O—CO—O—, —OCH₂—, —CH₂O—, —OCF₂—, —CF₂O—,    —(CH₂)_(n)—, —CF₂CF₂—, —CH═CH—, —CF═CF—, —CH═CH—OOC—, —OCO—CH═CH—,    —CO—S—, —S—CO—, —CS—S—, —S—CS—, —S—CSS— or —C≡C—,    -   preferably a single bond, —OOC—, —OOC—, —OCF₂—, —CF₂O—, or        —(CH₂)_(n)—,    -   more preferably a single bond, —OOC—, or —OOC—,

-   n denotes an integer between 2 and 8, preferably 2,

-   o and p denotes each and independently 0, 1 or 2, preferably 1,

-   X¹¹ and X²¹ denote independently from one another, in each    occurrence a single bond, —CO—O—, —O—CO—, —O—COO—, —O—, —CH═CH—,    —C≡C—, —CF₂—O—, —O—CF₂—, —CF₂—CF₂—, —CH₂—O—, —O—CH₂—, —CO—S—,    —S—CO—, —CS—S—, —S—CS—, —S—CSS— or —S—,    -   preferably, a single bond, —CO—O—, —O—CO—, —O—OOC—, or —O—,    -   more preferably a single bond or —O—,

-   Sp¹¹ and Sp²¹ denote each and independently, in each occurrence a    single bond or a spacer group comprising 1 to 20 C atoms, wherein    one or more non-adjacent and non-terminal CH₂ groups may also be    replaced by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —O—CO—, —S—CO—, —O—COO—,    —CO—S—, —CO—O—, —CF₂—, —CF₂O—, —OCF₂— —C(OH)—, —CH(alkyl)-,    —CH(alkenyl)-, —CH(alkoxyl)-, —CH(oxaalkyl)-, —CH═CH— or —C≡C—,    however in such a way that no two O-atoms are adjacent to one    another and no two groups selected from —O—CO—, —S—CO—, —O—OOC—,    —CO—S—, —CO—O— and —CH═CH— are adjacent to each other,    -   preferably alkylene having 1 to 20, preferably 1 to 12, C atoms,        which is optionally mono- or polysubstituted by F, Cl, Br, I or        CN,    -   more preferably straight-chain ethylene, propylene, butylene,        pentylene, hexylene, heptylene, octylene, nonylene, decylene,        undecylene, dodecylene,

-   R¹¹ denotes P,

-   R²¹ denotes P, or halogen, CN, optionally fluorinated alkyl or    alkenyl with up to 15 C atoms in which one or more non-adjacent    CH₂-groups may be replaced by —O—, —S—, —CO—, —C(O)O—, —O—C(O)—,    O—C(O)—O—, preferably P,

-   P each and independently from another in each occurrence a    polymerizable group.

The polymerizable groups P are groups that are suitable for apolymerisation reaction, such as, for example, free-radical or ionicchain polymerisation, polyaddition or polycondensation, or for apolymer-analogous reaction, for example addition or condensation onto amain polymer chain. Particular preference is given to groups for chainpolymerisation, in particular those containing a C═C double bond or—C≡C— triple bond, and groups which are suitable for polymerisation withring opening, such as, for example, oxetane or epoxide groups.

Preferred groups P are selected from the group consisting of

CH₂═CW²—(O)_(k3)—, CW¹═CH—CO—(O)_(k3)—, CW¹═CH—CO—NH—, CH₂═CW¹—CO—NH—,CH₃—CH═CH—O—, (CH₂═CH)₂CH—OCO—, (CH₂═CH—CH₂)₂CH—OCO—, (CH₂═CH)₂CH—O—,(CH₂═CH—CH₂)₂N—, (CH₂═CH—CH₂)₂N—CO—, HO—CW²W³—, HS—CW²W³—, HW²N—,HO—CW²W³—NH—, CH₂═CW¹—CO—NH—, CH₂═CH—(COO)_(k1)-Phe-(O)_(k2)—,CH₂═CH—(CO)_(k1)-Phe-(O)_(k2)—, Phe-CH═CH—, HOOC—, OCN— and W⁴W⁵W⁶Si—,wherein W¹ denotes H, F, Cl, CN, CF₃, phenyl or alkyl having 1 to 5 Catoms, in particular H, F, Cl or CH₃, W² and W³ each, independently ofone another, denote H or alkyl having 1 to 5 C atoms, in particular H,methyl, ethyl or n-propyl, W⁴, W⁵ and W⁶ each, independently of oneanother, denote Cl, oxaalkyl or oxacarbonylalkyl having 1 to 5 C atoms,W⁷ and W⁸ each, independently of one another, denote H, Cl or alkylhaving 1 to 5 C atoms, Phe denotes 1,4-phenylene, which is optionallysubstituted by one or more radicals L as defined above which are otherthan P-Sp-, k₁, k₂ and k₃ each, independently of one another, denote 0or 1, k₃ preferably denotes 1, and k₄ denotes an integer from 1 to 10.

Particularly preferred groups P and P^(a,b) are selected from the groupconsisting of CH₂═CW¹—CO—O—, in particular CH₂═CH—CO—O—,CH₂═C(CH₃)—CO—O— and CH₂═CF—CO—O—, furthermore CH₂═CH—O—,(CH₂═CH)₂CH—O—CO—, (CH₂═CH)₂CH—O—,

Very particularly preferred groups P and P^(a,b) are selected from thegroup consisting of acrylate, methacrylate, fluoroacrylate, furthermorevinyloxy, chloroacrylate, oxetane and epoxide groups, and of thesepreferably an acrylate or methacrylate group.

In another preferred embodiment, the polymerizable group P denotes theradical

wherein

-   Y denotes H, F, phenyl or optionally fluorinated alkyl having 1-12 C    atoms, preferably H, methyl, ethyl, propyl, butyl,    -   more preferably H or methyl,    -   in particular H,-   q and r denotes each and independently an integer from 0 to 8,    preferably q+r≥1 and ≤16, more preferably q and r each and    independently denotes an integer from 1 to 8, and-   P denotes acrylate or methacrylate,

The compounds of formula I are preferably selected from compounds of thesub-formulae I-1 to I-9.

wherein R¹¹, R²¹, A¹¹, X¹¹, X¹², Y¹¹, Y¹², Sp¹¹, and Sp¹² have one ofthe meanings as given above in formula I, A¹² to A²³ have one of themeanings for A, and Z¹¹ to Z²² have one of the meanings for Z as givenabove under formula I.

Further preferred compounds of formula I are selected from the compoundsof formulae I-1 to I-3.

Preferred compounds of formula I-1 to I-3 are selected from compounds offormulae I-1a to I-3a:

wherein R¹¹, R²¹, X¹¹, X²¹, Sp¹¹ and Sp²¹ have one of the meanings asgiven above in formula I, Z¹¹ and Z²¹ have one of the meanings for Z asgiven above under formula I, and A¹², A²¹ and A²² have one of themeanings for A, preferably A¹², A²¹ and A²² denote each andindependently a group consisting of 1,4-phenylene wherein one or two CHgroups may be replaced by N and wherein, in addition, one or more Hatoms may be replaced by L as given above under formula I, or a groupconsisting of trans-1,4-cyclohexylene, 1,4-cyclohexenylene, wherein, inaddition, one or more non-adjacent CH₂ groups may be replaced by —O—and/or —S— and wherein, in addition, one or more H atoms may be replacedby F.

Further preferred compounds of formula I are compounds of the followingsub-formula:

R¹¹, R²¹, X²¹, Sp¹¹ and Sp²¹ have one of the meanings as given above informula I, Z¹¹ and Z²¹ have one of the meanings for Z as given aboveunder formula I. In the above given preferred subformulae, the group

is each and independently

or denotes

furthermore

wherein L is preferably F, Cl, CH₃, OCH₃ and COCH₃ or alkylene having 1to 6 C Atoms, such as methyl, ethyl, propyl, butyl, pentyl, hexyl,cyclopropyl, cylobutyl, cyclopentyl, cyclohexyl, or X²¹-Sp²¹-R²¹.

Further preferred compounds of formulae I-2a-1 are those wherein Z¹¹denotes a single bond.

Further preferred compounds of formulae I-1a-1 to I-3a-1 are thosewherein X¹¹ and X²¹ denote each and independently a single bond, —O—,—CO—O— or —O—CO—, more preferably —O— or a single bond.

Further preferred compounds of formula I-1a-1 to I-3a-1 are thosewherein Sp¹¹ and Sp²¹ denote each and independently a single bond or—(CH₂)_(n)— wherein n is an integer between 1 and 8, more preferably 2and 6.

Further preferred compounds of formulae I-1a-1 to I-3a-1 are thosewherein R¹¹ and R²¹ denote each and independently acrylate, methacrylateor a group

wherein

-   Y denotes H, F, phenyl or optionally fluorinated alkyl having 1-12 C    atoms, preferably H, methyl, ethyl, propyl, butyl,    -   more preferably H or methyl,    -   in particular H,-   q and r denotes each and independently an integer from 0 to 8,    preferably q+r≥1 and ≤16, more preferably q and r each and    independently denotes an integer from 1 to 8.    Further preferred compounds of formulae I-1a-1 to I-3a-1 are those    wherein R¹¹ denotes a group

wherein

-   Y denotes H or methyl,    -   in particular H,-   q and r denotes each and independently an integer from 1 to 8,    preferably 1 or 2, and    wherein R¹¹ denotes acrylate or methacrylate.

Further preferred compounds of formulae I-1-1a-1 to I-3a-1 are thosewherein both groups R¹¹ and R²¹ denote acrylate or methacrylate.Preferred compounds of formulae I-3a-1 are compounds of the followingsub-formulae:

R¹¹, R²¹, X²¹, and Sp²¹ have one of the meanings as given above informula I, Z²¹ has one of the meanings for Z as given above underformula I, r, s, t and q denote each and independently from another aninteger from 1 to 8, Y denotes each and independently from each othermethyl or H, and

the group

is each and independently

or denotes

furthermore

wherein L is preferably F, Cl, CH₃, OCH₃ and COCH₃ or alkylene having 1to 6 C Atoms, such as methyl, ethyl, propyl, butyl, pentyl, hexyl,cyclopropyl, cylobutyl, cyclopentyl, cyclohexyl, or X²¹-Sp²¹-R²¹.

Further preferred compounds of formulae I-3a-1a are compounds of thefollowing sub-formulae:

wherein Sp²¹ has one of the meanings as given above in formula I and Ldenotes F, Cl, OCH₃ and COCH₃ or alkylene having 1 to 6 C Atoms,preferably methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclopropyl,cylobutyl, cyclopentyl, or cyclohexyl.

Further preferred compounds of formulae I-3a-1b are compounds of thefollowing sub-formulae:

wherein Sp²¹ has one of the meanings as given above in formula I and Ldenotes F, Cl, OCH₃ and COCH₃ or alkylene having 1 to 6 C Atoms,preferably methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclopropyl,cylobutyl, cyclopentyl, or cyclohexyl and s denotes an integer from 1 to8.

Further preferred compounds of formulae I-3a-1c are compounds of thefollowing sub-formulae:

wherein L denotes F, Cl, OCH₃ and COCH₃ or alkylene having 1 to 6 CAtoms, preferably methyl, ethyl, propyl, butyl, pentyl, hexyl,cyclopropyl, cylobutyl, cyclopentyl, or cyclohexyl, ands and t denotes each and independently an integer from 1 to 8,preferably s and t are identical.

The compounds of formula I and subformulae thereof are preferablysynthesised according to or in analogy to the procedures described in WO2017/102068 and JP 2006-6232809.

Preferred intermediate compounds (5) from which the compounds of formulaI are preferably synthesised, are obtainable or obtained according to orin analogy to the procedure described in the following scheme:

The compounds of formula I and subformulae thereof can be preferablyutilized in a mixture comprising one or more mesogenic orliquid-crystalline compounds.

Therefore, the present invention relates to the use compounds of formulaI and subformulae thereof in a liquid crystal mixture.

Further the present invention relates to liquid crystal mixturescomprising a photoalignment component A) comprising one or morephotoreactive mesogens of formula I, and a liquid-crystalline componentB), hereinafter also referred to as “LC host mixture”, comprising one ormore mesogenic or liquid-crystalline compounds.

The media according to the invention preferably comprise from 0.01 to10%, particularly preferably from 0.05 to 5% and most preferably from0.1 to 3% of component A) comprising compounds of formula I according tothe invention.

The media preferably comprise one, two or three, more preferably one ortwo and most preferably one compound of the formula I according to theinvention.

In a preferred embodiment component A) consists of compounds of formulaI.

In a preferred embodiment, the LC-host mixture (component B) accordingto the present invention comprises one or more, preferably two or more,low-molecular-weight (i.e. monomeric or unpolymerized) compounds. Thelatter are stable or unreactive with respect to a polymerisationreaction or photoalignment under the conditions used for thepolymerisation of the polymerizable compounds or photoalignment of thephotoreactive mesogen of formula I.

In principle, a suitable host mixture is any dielectrically negative orpositive LC mixture which is suitable for use in conventional VA, IPS orFFS displays.

Suitable LC mixtures are known to the person skilled in the art and aredescribed in the literature. LC media for VA displays having negativedielectric anisotropy are described in for example EP 1 378 557 A1.

Suitable LC mixtures having positive dielectric anisotropy which aresuitable for LCDs and especially for IPS displays are known, forexample, from JP 07-181 439 (A), EP 0 667 555, EP 0 673 986, DE 195 09410, DE 195 28 106, DE 195 28 107, WO 96/23 851, WO 96/28 521 andWO2012/079676.

Preferred embodiments of the liquid-crystalline medium having negativeor positive dielectric anisotropy according to the invention areindicated below and explained in more detail by means of the workingexamples.

The LC host mixture is preferably a nematic LC mixture, and preferablydoes not have a chiral LC phase.

In a preferred embodiment of the present invention the LC mediumcontains an LC host mixture with negative dielectric anisotropy.Preferred embodiments of such an LC medium, and the corresponding LChost mixture, are those of sections a)-z) below:

-   a) LC medium which comprises one or more compounds of the formulae    CY and/or PY:

-   -   wherein    -   a denotes 1 or 2,    -   b denotes 0 or 1,

denotes

-   -   R¹ and R² each, independently of one another, denote alkyl        having 1 to 12 C atoms, where, in addition, one or two        non-adjacent CH₂ groups may be replaced        -   by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O            atoms are not linked directly to one another, preferably            alkyl or alkoxy having 1 to 6 C atoms,    -   Z^(x) and Z^(y) each, independently of one another, denote        —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂O—, —CH₂O—, —O CH₂—, —CO—O—,        —O—CO—, —C₂F₄—, —CF═CF—, —CH═CH—CH₂O— or a single bond,        preferably a single bond,    -   L¹⁻⁴ each, independently of one another, denote F, Cl, OCF₃,        CF₃, CH₃, CH₂F, CHF₂.    -   Preferably, both L¹ and L² denote F or one of L¹ and L² denotes        F and the other denotes Cl, or both L³ and L⁴ denote F or one of        L³ and L⁴ denotes F and the other denotes Cl.    -   The compounds of the formula CY are preferably selected from the        group consisting of the following sub-formulae:

-   -   wherein a denotes 1 or 2, alkyl and alkyl* each, independently        of one another, denote a straight-chain alkyl radical having 1-6        C atoms, and alkenyl denotes a straight-chain alkenyl radical        having 2-6 C atoms, and (O) denotes an oxygen atom or a single        bond. Alkenyl preferably denotes CH₂═CH—, CH₂═CHCH₂CH₂—,        CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH—        or CH₃—CH═CH—(CH₂)₂—.    -   The compounds of the formula PY are preferably selected from the        group consisting of the following sub-formulae:

-   -   wherein alkyl and alkyl* each, independently of one another,        denote a straight-chain alkyl radical having 1-6 C atoms, and        alkenyl denotes a straight-chain alkenyl radical having 2-6 C        atoms, and (O) denotes an oxygen atom or a single bond. Alkenyl        preferably denotes CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,        CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or        CH₃—CH═CH—(CH₂)₂—.

-   b) LC medium which additionally comprises one or more compounds of    the following formula:

-   -   in which the individual radicals have the following meanings:

denotes

denotes

-   -   R³ and R⁴ each, independently of one another, denote alkyl        having 1 to 12 C atoms, in which, in addition, one or two        non-adjacent CH₂ groups may be replaced        -   by —O—, —CH═CH—, —CO—, —O—CO— or —CO—O— in such a way that O            atoms are not linked directly to one another,    -   Z^(y)        -   denotes —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—,            —CO—O—, —O—CO—, —C₂F₄—, —CF═CF—, —CH═CH—CH₂O— or a single            bond, preferably a single bond.    -   The compounds of the formula ZK are preferably selected from the        group consisting of the following sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,        denote a straight-chain alkyl radical having 1-6 C atoms, and        alkenyl denotes a straight-chain alkenyl radical having 2-6 C        atoms. Alkenyl preferably denotes CH₂═CH—, CH₂═CHCH₂CH₂—,        CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH—        or CH₃—CH═CH—(CH₂)₂—.    -   Especially preferred are compounds of formula ZK1 and ZK3.    -   Particularly preferred compounds of formula ZK are selected from        the following sub-formulae:

-   -   wherein the propyl, butyl and pentyl groups are straight-chain        groups.    -   Most preferred are compounds of formula ZK1a and ZK3a.

-   c) LC medium which additionally comprises one or more compounds of    the following formula:

-   -   in which the individual radicals on each occurrence, identically        or differently, have the following meanings:    -   R⁵ and R⁶ each, independently of one another, denote alkyl        having 1 to 12 C atoms, where, in addition, one or two        non-adjacent CH₂ groups may be replaced by —O—, —CH═CH—, —CO—,        —OCO— or —COO— in such a way that O atoms are not linked        directly to one another, preferably alkyl or alkoxy having 1 to        6 C atoms,

denotes

denotes

and

-   -   e denotes 1 or 2.    -   The compounds of the formula DK are preferably selected from the        group consisting of the following sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,        denote a straight-chain alkyl radical having 1-6 C atoms, and        alkenyl denotes a straight-chain alkenyl radical having 2-6 C        atoms. Alkenyl preferably denotes CH₂═CH—, CH₂═CHCH₂CH₂—,        CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH—        or CH₃—CH═CH—(CH₂)₂—.

-   d) LC medium which additionally comprises one or more compounds of    the following formula:

-   -   in which the individual radicals have the following meanings:

-   -   denotes

-   -   with at least one ring F being different from cyclohexylene,    -   f denotes 1 or 2,    -   R¹ and R² each, independently of one another, denote alkyl        having 1 to 12 C atoms, where, in addition, one or two        non-adjacent CH₂ groups may be replaced        -   by —O—, —CH═CH—, —CO—, —OCO— or —COO— in such a way that O            atoms are not linked directly to one another,    -   Z^(x)        -   denotes —CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —O CH₂—,            —CO—O—, —O—CO—, —C₂F₄—, —CF═CF—, —CH═CH—CH₂O— or a single            bond, preferably a single bond,    -   L¹ and L² each, independently of one another, denote F, Cl,        OCF₃, CF₃, CH₃, CH₂F, CHF₂.    -   Preferably, both radicals L¹ and L² denote F or one of the        radicals L¹ and L² denotes F and the other denotes Cl.    -   The compounds of the formula LY are preferably selected from the        group consisting of the following sub-formulae:

-   -   in which R¹ has the meaning indicated above, alkyl denotes a        straight-chain alkyl radical having 1-6 C atoms, (0) denotes an        oxygen atom or a single bond, and v denotes an integer from 1        to 6. R¹ preferably denotes straight-chain alkyl having 1 to 6 C        atoms or straight-chain alkenyl having 2 to 6 C atoms, in        particular CH₃, C₂H₅, n-C₃H₇, n-C₄H₉, n-C₅H₁₁, CH₂═CH—,        CH₂═CHCH₂CH₂—, CH₃—CH═CH—, CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—,        CH₃—(CH₂)₃—CH═CH— or CH₃—CH═CH—(CH₂)₂—.

-   e) LC medium which additionally comprises one or more compounds    selected from the group consisting of the following formulae:

-   -   in which alkyl denotes C₁₋₆-alkyl, L^(x) denotes H or F, and X        denotes F, Cl, OCF₃, OCHF₂ or OCH═CF₂. Particular preference is        given to compounds of the formula G1 in which X denotes F.

-   f) LC medium which additionally comprises one or more compounds    selected from the group consisting of the following formulae:

-   -   in which R⁵ has one of the meanings indicated above for R¹,        alkyl denotes C1-6-alkyl, d denotes 0 or 1, and z and m each,        independently of one another, denote an integer from 1 to 6. R⁵        in these compounds is particularly preferably C₁₋₆-alkyl or        -alkoxy or C₂₋₆-alkenyl, d is preferably 1. The LC medium        according to the invention preferably comprises one or more        compounds of the above-mentioned formulae in amounts of 5% by        weight.

-   g) LC medium which additionally comprises one or more biphenyl    compounds selected from the group consisting of the following    formulae:

-   -   in which alkyl and alkyl* each, independently of one another,        denote a straight-chain alkyl radical having 1-6 C atoms, and        alkenyl and alkenyl* each, independently of one another, denote        a straight-chain alkenyl radical having 2-6 C atoms. Alkenyl and        alkenyl* preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,        CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or        CH₃—CH═CH—(CH₂)₂—.    -   The proportion of the biphenyls of the formulae B1 to B3 in the        LC mixture is preferably at least 3% by weight, in particular        ≥5% by weight.    -   The compounds of the formula B2 are particularly preferred.    -   The compounds of the formulae B1 to B3 are preferably selected        from the group consisting of the following sub-formulae:

-   -   in which alkyl* denotes an alkyl radical having 1-6 C atoms. The        medium according to the invention particularly preferably        comprises one or more compounds of the formulae B1a and/or B2e.

-   h) LC medium which additionally comprises one or more terphenyl    compounds of the following formula:

-   -   in which R⁵ and R⁶ each, independently of one another, have one        of the meanings indicated above, and

-   -   each, independently of one another, denote

-   -   in which L⁵ denotes F or Cl, preferably F, and L⁶ denotes F, Cl,        OCF₃, CF₃, CH₃, CH₂F or CHF₂, preferably F.    -   The compounds of the formula T are preferably selected from the        group consisting of the following sub-formulae:

-   -   in which R denotes a straight-chain alkyl or alkoxy radical        having 1-7 C atoms, R* denotes a straight-chain alkenyl radical        having 2-7 C atoms, (O) denotes an oxygen atom or a single bond,        and m denotes an integer from 1 to 6. R* preferably denotes        CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—, CH₃—CH₂—CH═CH—,        CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or CH₃—CH═CH—(CH₂)₂—.    -   R preferably denotes methyl, ethyl, propyl, butyl, pentyl,        hexyl, methoxy, ethoxy, propoxy, butoxy or pentoxy.    -   The LC medium according to the invention preferably comprises        the terphenyls of the formula T and the preferred sub-formulae        thereof in an amount of 0.5-30% by weight, in particular 1-20%        by weight.    -   Particular preference is given to compounds of the formulae T1,        T2, T3 and T21. In these compounds, R preferably denotes alkyl,        furthermore alkoxy, each having 1-5 C atoms.    -   The terphenyls are preferably employed in mixtures according to        the invention if the Δn value of the mixture is to be ≥0.1.        Preferred mixtures comprise 2-20% by weight of one or more        terphenyl compounds of the formula T, preferably selected from        the group of compounds T1 to T22.

-   i) LC medium which additionally comprises one or more compounds    selected from the group consisting of the following formulae:

-   -   in which R¹ and R² have the meanings indicated above and        preferably each, independently of one another, denote        straight-chain alkyl having 1 to 6 C atoms or straight-chain        alkenyl having 2 to 6 C atoms.    -   Preferred media comprise one or more compounds selected from the        formulae O1, O3 and O4.

-   k) LC medium which additionally comprises one or more compounds of    the following formula:

-   -   in which

denotes

-   -   R⁹ denotes H, CH₃, C₂H₅ or n-C₃H₇, (F) denotes an optional        fluorine substituent, and q denotes 1, 2 or 3, and R⁷ has one of        the meanings indicated for R¹, preferably in amounts of >3% by        weight, in particular ≥5% by weight and very particularly        preferably 5-30% by weight.    -   Particularly preferred compounds of the formula FI are selected        from the group consisting of the following sub-formulae:

-   -   in which R⁷ preferably denotes straight-chain alkyl, and R⁹        denotes CH₃, C₂H₅ or n-C₃H₇. Particular preference is given to        the compounds of the formulae FI1, FI2 and FI3.

-   l) LC medium which additionally comprises one or more compounds    selected from the group consisting of the following formulae:

-   -   in which R⁸ has the meaning indicated for R¹, and alkyl denotes        a straight-chain alkyl radical having 1-6 C atoms.

-   m) LC medium which additionally comprises one or more compounds    which contain a tetrahydronaphthyl or naphthyl unit, such as, for    example, the compounds selected from the group consisting of the    following formulae:

-   -   in which    -   R¹⁰ and R¹¹ each, independently of one another, denote alkyl        having 1 to 12 C atoms, where, in addition, one or two        non-adjacent CH₂ groups may be replaced        -   by —O—, —CH═CH—, —CO—, —OCO— or —OOC— in such a way that O            atoms are not linked directly to one another, preferably            alkyl or alkoxy having 1 to 6 C atoms,    -   and R¹⁰ and R¹¹ preferably denote straight-chain alkyl or alkoxy        having 1 to 6 C atoms or straight-chain alkenyl having 2 to 6 C        atoms, and    -   Z¹ and Z² each, independently of one another,        -   denote —C₂H₄—, —CH═CH—, —(CH₂)₄—, —(CH₂)₃O—, —O(CH₂)₃—,            —CH═CH—        -   CH₂CH₂—, —CH₂CH₂CH═CH—, —CH₂O—, —OCH₂—, —CO O—, —O—        -   CO—, —C₂F₄—, —CF═CF—, —CF═CH—, —CH═CF—, —CH₂— or a single            bond.

-   n) LC medium which additionally comprises one or more    difluoro-dibenzochromans and/or chromans of the following formulae:

-   -   in which    -   R¹¹ and R¹² each, independently of one another, have one of the        meanings indicated above for R¹¹ under formula N1    -   ring M is trans-1,4-cyclohexylene or 1,4-phenylene,    -   Z^(m) —C₂H₄—, —CH₂O—, —OCH₂—, —CO—O— or —O—CO—,    -   c is 0, 1 or 2,    -   preferably in amounts of 3 to 20% by weight, in particular in        amounts of 3 to 15% by weight.    -   Particularly preferred compounds of the formulae BC, CR and RC        are selected from the group consisting of the following        sub-formulae:

-   -   in which alkyl and alkyl* each, independently of one another,        denote a straight-chain alkyl radical having 1-6 C atoms, (O)        denotes an oxygen atom or a single bond, c is 1 or 2, and        alkenyl and alkenyl* each, independently of one another, denote        a straight-chain alkenyl radical having 2-6 C atoms. Alkenyl and        alkenyl* preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,        CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or        CH₃—CH═CH—(CH₂)₂—.    -   Very particular preference is given to mixtures comprising one,        two or three compounds of the formula BC-2.

-   o) LC medium which additionally comprises one or more fluorinated    phenanthrenes and/or dibenzofurans of the following formulae:

-   -   in which R¹¹ and R¹² each, independently of one another, have        one of the meanings indicated above for R¹¹ under formula N1, b        denotes 0 or 1, L denotes F, and r denotes 1, 2 or 3.    -   Particularly preferred compounds of the formulae PH and BF are        selected from the group consisting of the following        sub-formulae:

-   -   in which R and R′ each, independently of one another, denote a        straight-chain alkyl or alkoxy radical having 1-7 C atoms.

-   p) LC medium which additionally comprises one or more monocyclic    compounds of the following formula

-   -   wherein    -   R¹ and R² each, independently of one another, denote alkyl        having 1 to 12 C atoms, where, in addition, one or two        non-adjacent CH₂ groups may be replaced        -   by —O—, —CH═CH—, —CO—, —OCO— or —OOC— in such a way that O            atoms are not linked directly to one another, preferably            alkyl or alkoxy having 1 to 6 C atoms,    -   L¹ and L² each, independently of one another, denote F, Cl,        OCF₃, CF₃, CH₃, CH₂F, CHF₂.    -   Preferably, both L¹ and L² denote F or one of L¹ and L² denotes        F and the other denotes Cl,    -   The compounds of the formula Y are preferably selected from the        group consisting of the following sub-formulae:

-   -   in which, Alkyl and Alkyl* each, independently of one another,        denote a straight-chain alkyl radical having 1-6 C atoms, Alkoxy        denotes a straight-chain alkoxy radical having 1-6 C atoms,        Alkenyl and Alkenyl* each, independently of one another, denote        a straight chain alkenyl radical having 2-6 C atoms, and O        denotes an oxygen atom or a single bond. Alkenyl and Alkenyl*        preferably denote CH₂═CH—, CH₂═CHCH₂CH₂—, CH₃—CH═CH—,        CH₃—CH₂—CH═CH—, CH₃—(CH₂)₂—CH═CH—, CH₃—(CH₂)₃—CH═CH— or        CH₃—CH═CH—(CH₂)₂—.    -   Particularly preferred compounds of the formula Y are selected        from the group consisting of the following sub-formulae:

-   -   wherein Alkoxy preferably denotes straight-chain alkoxy with 3,        4, or 5 C atoms.

-   q) LC medium which, apart from the stabilisers according to the    invention, in particular of the formula I or sub-formulae thereof    and the comonomers, comprises no compounds which contain a terminal    vinyloxy group (—O—CH═CH₂).

-   r) LC medium which comprises 1 to 5, preferably 1, 2 or 3,    stabilisers, preferably selected from stabilisers according to the    invention, in particular of the formula I or sub-formulae thereof.

-   s) LC medium in which the proportion of stabilisers, in particular    of the formula I or sub-formulae thereof, in the mixture as a whole    is 1 to 1500 ppm, preferably 100 to 1000 ppm.

-   t) LC medium which comprises 1 to 8, preferably 1 to 5, compounds of    the formulae CY1, CY2, PY1 and/or PY2. The proportion of these    compounds in the mixture as a whole is preferably 5 to 60%,    particularly preferably 10 to 35%. The content of these individual    compounds is preferably in each case 2 to 20%.

-   u) LC medium which comprises 1 to 8, preferably 1 to 5, compounds of    the formulae CY9, CY10, PY9 and/or PY10. The proportion of these    compounds in the mixture as a whole is preferably 5 to 60%,    particularly preferably 10 to 35%. The content of these individual    compounds is preferably in each case 2 to 20%.

-   v) LC medium which comprises 1 to 10, preferably 1 to 8, compounds    of the formula ZK, in particular compounds of the formulae ZK1, ZK2    and/or ZK6. The proportion of these compounds in the mixture as a    whole is preferably 3 to 25%, particularly preferably 5 to 45%. The    content of these individual compounds is preferably in each case 2    to 20%.

-   w) LC medium in which the proportion of compounds of the formulae    CY, PY and ZK in the mixture as a whole is greater than 70%,    preferably greater than 80%.

-   x) LC medium in which the LC host mixture contains one or more    compounds containing an alkenyl group, preferably selected from the    group consisting of formula CY, PY and LY, wherein one or both of R¹    and R² denote straight-chain alkenyl having 2-6 C atoms, formula ZK    and DK, wherein one or both of R³ and R⁴ or one or both of R⁵ and R⁶    denote straight-chain alkenyl having 2-6 C atoms, and formula B2 and    B3, very preferably selected from formulae CY15, CY16, CY24, CY32,    PY15, PY16, ZK3, ZK4, DK3, DK6, B2 and B3, most preferably selected    from formulae ZK3, ZK4, B2 and B3. The concentration of these    compounds in the LC host mixture is preferably from 2 to 70%, very    preferably from 3 to 55%.

-   y) LC medium which contains one or more, preferably 1 to 5,    compounds selected of formula PY1-PY8, very preferably of formula    PY2. The proportion of these compounds in the mixture as a whole is    preferably 1 to 30%, particularly preferably 2 to 20%. The content    of these individual compounds is preferably in each case 1 to 20%.

-   z) LC medium which contains one or more, preferably 1, 2 or 3,    compounds of formula T2. The content of these compounds in the    mixture as a whole is preferably 1 to 20%.

In another preferred embodiment of the present invention the LC mediumcontains an LC host mixture with positive dielectric anisotropy.Preferred embodiments of such an LC medium, and the corresponding LChost mixture, are those of sections aa)-mmm) below:

-   aa) LC-medium, characterised in that it comprises one or more    compounds selected from the group of compounds of the formulae II    and III

-   -   wherein    -   R²⁰ each, identically or differently, denote a halogenated or        unsubstituted alkyl or alkoxy radical having 1 to 15 C atoms,        where, in addition, one or more CH₂ groups in these radicals may        each be replaced, independently of one another, by —C≡C—,        —CF₂O—, —CH═CH—, —⋄—, —⋄⋄—, —O—, —CO—O— or —O—CO— in such a way        that O atoms are not linked directly to one another,    -   X²⁰ each, identically or differently, denote F, Cl, CN, SF₅,        SCN, NCS, a halogenated alkyl radical, a halogenated alkenyl        radical, a halogenated alkoxy radical or a halogenated        alkenyloxy radical, each having up to 6 C atoms, and    -   Y²⁰⁻²⁴ each, identically or differently, denote H or F;    -   W denotes H or methyl,

each, independently of one another, denote

-   -   The compounds of the formula II are preferably selected from the        following formulae:

-   -   wherein R²⁰ and X²⁰ have the meanings indicated above.    -   R²⁰ preferably denotes alkyl having 1 to 6 C atoms. X²⁰        preferably denotes F. Particular preference is given to        compounds of the formulae IIa and IIb, in particular compounds        of the formulae IIa and IIb wherein X denotes F.    -   The compounds of the formula III are preferably selected from        the following formulae:

-   -   wherein R²⁰ and X²⁰ have the meanings indicated above.    -   R²⁰ preferably denotes alkyl having 1 to 6 C atoms. X²⁰        preferably denotes F. Particular preference is given to        compounds of the formulae IIIa and IIIe, in particular compounds        of the formula IIIa;

-   bb) LC-medium additionally comprising one or more compounds selected    from the following formulae:

-   -   wherein    -   R²⁰, X²⁰, W and Y²⁰⁻²³ have the meanings indicated above under        formula II, and    -   Z²⁰ denotes —C₂H₄—, —(CH₂)₄—, —CH═CH—,        -   —CF═CF, —C₂F₄—, —CH₂CF₂—, —CF₂CH₂—, —CH₂O—, —OCH₂—, —OOC— or            —OCF₂—, in formulae V and VI also a single bond, in formulae            V and VIII also —CF₂O—,    -   r denotes 0 or 1, and    -   s denotes 0 or 1;    -   The compounds of the formula IV are preferably selected from the        following formulae:

-   -   wherein R²⁰ and X²⁰ have the meanings indicated above.    -   R²⁰ preferably denotes alkyl having 1 to 6 C atoms. X²⁰        preferably denotes F or OCF₃, furthermore OCF═CF₂ or Cl;    -   The compounds of the formula V are preferably selected from the        following formulae:

-   -   wherein R²⁰ and X²⁰ have the meanings indicated above.    -   R²⁰ preferably denotes alkyl having 1 to 6 C atoms. X²⁰        preferably denotes F and OCF₃, furthermore OCHF₂, CF₃, OCF═CF₂        and OCH═CF₂;    -   The compounds of the formula VI are preferably selected from the        following formulae:

-   -   wherein R²⁰ and X²⁰ have the meanings indicated above.    -   R²⁰ preferably denotes alkyl having 1 to 6 C atoms. X²⁰        preferably denotes F, furthermore OCF₃, CF₃, CF═CF₂, OCHF₂ and        OCH═CF₂;    -   The compounds of the formula VII are preferably selected from        the following formulae:

-   -   wherein R²⁰ and X²⁰ have the meanings indicated above.    -   R²⁰ preferably denotes alkyl having 1 to 6 C atoms. X²⁰        preferably denotes F, furthermore OCF₃, OCHF₂ and OCH═CF₂.

-   cc) The medium additionally comprises one or more compounds selected    from the formulae ZK1 to ZK10 given above. Especially preferred are    compounds of formula ZK1 and ZK3. Particularly preferred compounds    of formula ZK are selected from the sub-formulae ZK1a, ZK1 b, ZK1c,    ZK3a, ZK3b, ZK3c and ZK3d.

-   dd) The medium additionally comprises one or more compounds selected    from the formulae DK1 to DK12 given above. Especially preferred    compounds are DK3.

-   ee) The medium additionally comprises one or more compounds selected    from the following formulae:

-   -   wherein X²⁰ has the meanings indicated above, and    -   L denotes H or F,    -   “alkenyl” denotes C₂₋₆-alkenyl.

-   ff) The compounds of the formulae DK-3a and IX are preferably    selected from the following formulae:

-   -   wherein “alkyl” denotes C₁₋₆-alkyl, preferably n-C₃H₇, n-C₄H₉ or        n-C₅H₁₁, in particular n-C₃H₇.

-   gg) The medium additionally comprises one or more compounds selected    from the formulae B1, B2 and B3 given above, preferably from the    formula B2. The compounds of the formulae B1 to B3 are particularly    preferably selected from the formulae B1a, B2a, B2b and B2c.

-   hh) The medium additionally comprises one or more compounds selected    from the following formula:

-   -   wherein L²⁰ denotes H or F, and R²¹ and R²² each, identically or        differently, denote n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or        alkenyl, each having up to 6 C atoms, and preferably each,        identically or differently, denote alkyl having 1 to 6 C atoms.

-   ii) The medium comprises one or more compounds of the following    formulae:

-   -   Wherein W, R²⁰, X²⁰ and Y²⁰⁻²³ have the meanings indicated in        formula III, and

each, independently of one another, denote

-   -   and

denotes

-   -   The compounds of the formulae XI and XII are preferably selected        from the following formulae:

-   -   wherein R²⁰ and X²⁰ have the meaning indicated above and        preferably R²⁰ denotes alkyl having 1 to 6 C atoms and X²⁰        denotes F.    -   The mixture according to the invention particularly preferably        comprises at least one compound of the formula XIIa and/or XIIe.

-   jj) The medium comprises one or more compounds of formula T given    above, preferably selected from the group of compounds of the    formulae T21 to T23 and T25 to T27.    -   Particular preference is given to the compounds of the formulae        T21 to T23. Very particular preference is given to the compounds        of the formulae

-   kk) The medium comprises one or more compounds selected from the    group of formulae DK9, DK10 and DK11 given above.-   ll) The medium additionally comprises one or more compounds selected    from the following formulae:

-   -   wherein R²⁰ and X²⁰ each, independently of one another, have one        of the meanings indicated above, and Y²⁰⁻²³ each, independently        of one another, denote H or F. X²⁰ is preferably F, Cl, CF₃,        OCF₃ or OCHF₂. R²⁰ preferably denotes alkyl, alkoxy, oxaalkyl,        fluoroalkyl or alkenyl, each having up to 6 C atoms.    -   The mixture according to the invention particularly preferably        comprises one or more compounds of the formula XVIII-a,

-   -   wherein R²⁰ has the meanings indicated above. R²⁰ preferably        denotes straight-chain alkyl, in particular ethyl, n-propyl,        n-butyl and n-pentyl and very particularly preferably n-propyl.        The compound(s) of the formula XVIII, in particular of the        formula XVIII-a, is (are) preferably employed in the mixtures        according to the invention in amounts of 0.5-20% by weight,        particularly preferably 1-15% by weight.

-   mm) The medium additionally comprises one or more compounds of the    formula XIX,

-   -   wherein R²⁰, X²⁰ and Y²⁰⁻²⁵ have the meanings indicated in        formula I, s denotes 0 or 1, and

denotes

-   -   In the formula XIX, X²⁰ may also denote an alkyl radical having        1-6 C atoms or an alkoxy radical having 1-6 C atoms. The alkyl        or alkoxy radical is preferably straight-chain.    -   R²⁰ preferably denotes alkyl having 1 to 6 C atoms. X²⁰        preferably denotes F;    -   The compounds of the formula XIX are preferably selected from        the following formulae:

-   -   wherein R²⁰, X²⁰ and Y²⁰ have the meanings indicated above. R²⁰        preferably denotes alkyl having 1 to 6 C atoms. X²⁰ preferably        denotes F, and Y²⁰ is preferably F;

is preferably

-   -   R²⁰ is straight-chain alkyl or alkenyl having 2 to 6 C atoms;

-   nn) The medium comprises one or more compounds of the formulae G1 to    G4 given above, preferably selected from G1 and G2 wherein alkyl    denotes C₁₋₆-alkyl, L^(x) denotes H and X denotes F or Cl. In G2, X    particularly preferably denotes Cl.

-   oo) The medium comprises one or more compounds of the following    formulae:

-   -   wherein R²⁰ and X²⁰ have the meanings indicated above. R²⁰        preferably denotes alkyl having 1 to 6 C atoms. X²⁰ preferably        denotes F. The medium according to the invention particularly        preferably comprises one or more compounds of the formula XXII        wherein X²⁰ preferably denotes F. The compound(s) of the        formulae XX-XXII is (are) preferably employed in the mixtures        according to the invention in amounts of 1-20% by weight,        particularly preferably 1-15% by weight. Particularly preferred        mixtures comprise at least one compound of the formula XXII.

-   pp) The medium comprises one or more compounds of the following    pyrimidine or pyridine compounds of the formulae

-   -   wherein R²⁰ and X²⁰ have the meanings indicated above. R²⁰        preferably denotes alkyl having 1 to 6 C atoms. X²⁰ preferably        denotes F. The medium according to the invention particularly        preferably comprises one or more compounds of the formula M-1,        wherein X²⁰ preferably denotes F. The compound(s) of the        formulae M-1-M-3 is (are) preferably employed in the mixtures        according to the invention in amounts of 1-20% by weight,        particularly preferably 1-15% by weight.

Further preferred embodiments are indicated below:

-   qq) The medium comprises two or more compounds of the formula XII,    in particular of the formula XIIe;-   rr) The medium comprises 2-30% by weight, preferably 3-20% by    weight, particularly preferably 3-15% by weight, of compounds of the    formula XII;-   ss) Besides the compounds of the formulae XII, the medium comprises    further compounds selected from the group of the compounds of the    formulae II, III, IX-XIII, XVII and XVIII;-   tt) The proportion of compounds of the formulae II, III, IX-XI,    XIII, XVII and XVIII in the mixture as a whole is 40 to 95% by    weight;-   uu) The medium comprises 10-50% by weight, particularly preferably    12-40% by weight, of compounds of the formulae II and/or III;-   vv) The medium comprises 20-70% by weight, particularly preferably    25-65% by weight, of compounds of the formulae IX-XIII;-   ww) The medium comprises 4-30% by weight, particularly preferably    5-20% by weight, of compounds of the formula XVII;-   xx) The medium comprises 1-20% by weight, particularly preferably    2-15% by weight, of compounds of the formula XVIII;-   yy) The medium comprises at least two compounds of the formulae

-   zz) The medium comprises at least two compounds of the formulae

aaa) The medium comprises at least two compounds of the formula XIIa andat least two compounds of the formula XIIe.

-   bbb) The medium comprises at least one compound of the formula XIIa    and at least one compound of the formula XIIe and at least one    compound of the formula IIIa.-   ccc) The medium comprises at least two compounds of the formula XIIa    and at least two compounds of the formula XIIe and at least one    compound of the formula IIIa.-   ddd) The medium comprises in total ≥25% by weight, preferably ≥30%    by weight, of one or more compounds of the formula XII.-   eee) The medium comprises ≥20% by weight, preferably ≥24% by weight,    preferably 25-60% by weight, of compounds of the formula ZK3, in    particular the compound of the formula ZK3a,

-   fff) The medium comprises at least one compound selected from the    group of compounds ZK3a, ZK3b and ZK3c, preferably ZK3a, in    combination with compound ZK3d

-   ggg) The medium comprises at least one compound of the formula    DPGU-n-F.-   hhh) The medium comprises at least one compound of the formula    CDUQU-n-F.-   iii) The medium comprises at least one compound of the formula    CPU-n-OXF.-   jjj) The medium comprises at least one compound of the formula    CPGU-3-OT.-   kkk) The medium comprises at least one compound of the formula    PPGU-n-F.-   lll) The medium comprises at least one compound of the formula    PGP-n-m, preferably two or three compounds.-   mmm) The medium comprises at least one compound of the formula    PGP-2-2V having the structure

-   -   In a preferred embodiment, the liquid crystal mixture according        to the present invention further comprises a polymerizable        component C) comprising one or more polymerizable compounds.    -   The polymerizable compounds can be selected from isotropic or        mesogenic polymerizable compounds known to the skilled person in        the art.    -   Preferably, the polymerizable component C) comprises one or more        polymerizable compounds of formula P,        P^(a)-(Sp^(a))_(s1)-A²-(Z^(a)-A¹)_(n2)-(Sp^(b))_(s2)—Pb  P        wherein the individual radicals have the following meanings:    -   P^(a), P^(b) each, independently of one another, denote a        polymerizable group,    -   Sp^(a), Sp^(b) on each occurrence, identically or differently,        denote a spacer group,    -   s1, s2 each, independently of one another, denote 0 or 1,    -   A¹, A² each, independently of one another, denote a radical        selected from the following groups:        -   a) the group consisting of trans-1,4-cyclohexylene,            1,4-cyclohexenylene and 4,4″-bicyclohexylene, wherein, in            addition, one or more non-adjacent CH₂ groups may be            replaced by —O— and/or —S— and wherein, in addition, one or            more H atoms may be replaced by F,        -   b) the group consisting of 1,4-phenylene and 1,3-phenylene,            wherein, in addition, one or two CH groups may be replaced            by N and wherein, in addition, one or more H atoms may be            replaced by L,        -   c) the group consisting of tetrahydropyran-2,5-diyl,            1,3-dioxane-2,5-diyl, tetrahydrofuran-2,5-diyl,            cyclobutane-1,3-diyl, piperidine-1,4-diyl,            thiophene-2,5-diyl and selenophene-2,5-diyl, each of which            may also be mono- or polysubstituted by L,        -   d) the group consisting of saturated, partially unsaturated            or fully unsaturated, and optionally substituted, polycyclic            radicals having 5 to 20 cyclic C atoms, one or more of which            may, in addition, be replaced by heteroatoms, preferably            selected from the group consisting of

-   -   -   -   where, in addition, one or more H atoms in these                radicals may be replaced by L, and/or one or more double                bonds may be replaced by single bonds, and/or one or                more CH groups may be replaced by N,

    -   n2 denotes 0, 1, 2 or 3,

    -   Z^(a) in each case, independently of one another, denotes        —CO—O—, —O—CO—, —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂—, or —(CH₂)_(n)—,        where n is 2, 3 or 4, —O—, —CO—, —C(R^(y)R^(z))—, —CH₂CF₂—,        —CF₂CF₂— or a single bond,

    -   L on each occurrence, identically or differently, denotes F, Cl,        CN, SCN, SF₅ or straight-chain or branched, in each case        optionally fluorinated, alkyl, alkoxy, alkylcarbonyl,        alkoxycarbonyl, alkylcarbonyloxy or al koxycarbonyloxy having 1        to 12 C atoms,

    -   R^(y), R^(z) each, independently of one another, denote H, F or        straight-chain or branched alkyl having 1 to 12 C atoms,        wherein, in addition, one or more H atoms may be replaced by F,

    -   M denotes —O—, —S—, —CH₂—, —CHY¹— or —CY¹Y²—, and

    -   Y¹ and Y² each, independently of one another, have one of the        meanings indicated above for RY or denote Cl or CN.

Preferred spacer groups Sp^(a,b) are selected from the formula Sp″-X″,so that the radicals P-Sp— and P^(a/b)-Sp^(a/b)— conforms to theformulae P-Sp″-X″— and P^(a/b)-Sp″-X″—, respectively, wherein

-   -   Sp″ denotes alkylene having 1 to 20, preferably 1 to 12, C        atoms, which is optionally mono- or polysubstituted by F, Cl,        Br, I or CN and wherein, in addition, one or more non-adjacent        CH₂ groups may each be replaced, independently of one another,        by —O—, —S—, —NH—, —N(R⁰)—, —Si(R⁰⁰R⁰⁰⁰)—, —CO—, —CO—O—, —O—CO—,        —O—CO—O—, —S—CO—, —CO—S—, —N(R⁰⁰)—CO—O—, —O—CO—N(R⁰⁰)—,        —N(R⁰⁰)—CO—N(R⁰⁰)—, —CH═CH— or —C≡C— in such a way that O and/or        S atoms are not linked directly to one another,    -   X″ denotes —O—, —S—, —CO—, —CO—O—, —O—CO—, —O—CO—O—,        —CO—N(R⁰⁰)—, —N(R⁰⁰)—CO—, —N(R⁰⁰)—CO—N(R⁰⁰)—, —OCH₂—, —CH₂O—,        —SCH₂—, —CH₂S—, —CF₂O—, —OCF₂—, —CF₂S—, —SCF₂—, —CF₂CH₂—,        —CH₂CF₂—, —CF₂CF₂—, —CH═N—, —N═CH—, —N═N—, —CH═CR⁰—, —CY³═CY⁴—,        —C≡C—, —CH═CH—CO—O—, —O—CO—CH═CH— or a single bond,    -   R⁰, R⁰⁰    -   and R⁰⁰⁰ each, independently of one another, denote H or alkyl        having 1 to 12 C atoms, and    -   Y³ and Y⁴ each, identically or differently, denote H, F, Cl or        CN.

X″ is preferably —O—, —S—, —CO—, —C(O)O—, —OC(O)—, —O—C(O)O—, —CO—NR⁰—,—NR⁰—CO—, —NR⁰—CO—NR⁰— or a single bond.

Typical spacer groups Sp″ are, for

example, —(CH₂)_(p1)—, —(CH₂CH₂O)_(q1)—CH₂CH₂—, —CH₂CH₂—S—CH₂CH₂—,—CH₂CH₂—NH—CH₂CH₂— or —(SiR⁰⁰R⁰⁰⁰—O)_(p1)—, wherein p1 is an integerfrom 1 to 12, q1 is an integer from 1 to 3, and R⁰⁰ and R⁰⁰⁰ have themeanings indicated above.

-   -   Particularly preferred groups -Sp″-X″— are —(CH₂)_(p1)—,        —(CH₂)_(p1)—O—, —(CH₂)_(p1)—O—CO—, —(CH₂)_(p1)—O—CO—O—, wherein        p1 and q1 have the meanings indicated above.    -   Particularly preferred groups Sp″ are, for example, in each case        straight-chain ethylene, propylene, butylene, pentylene,        hexylene, heptylene, octylene, nonylene, decylene, undecylene,        dodecylene, octadecylene, ethyleneoxyethylene,        methyleneoxybutylene, ethylenethioethylene,        ethylene-N-methyliminoethylene, 1-methylalkylene, ethenylene,        propenylene and butenylene.    -   Particularly preferred monomers of formula P are the following:

wherein the individual radicals have the following meanings:

-   P¹ to P³ each, independently of one another, denote a polymerizable    group as defined for formula P, preferably an acrylate,    methacrylate, fluoroacrylate, oxetane, vinyloxy or epoxide group,-   Sp¹ to Spa each, independently of one another, denote a single bond    or a spacer group, preferably having one of the meanings indicated    above and below for Spa, and particularly preferably —(CH₂)_(p1)—,    —(CH₂)_(p1)—O—, —(CH₂)_(p1)—CO—O— or —(CH₂)_(p1)—O—CO—O—, wherein p1    is an integer from 1 to 12, and where the linking to the adjacent    ring in the last-mentioned groups takes place via the O atom,    -   where, in addition, one or more of the radicals P¹-Sp¹—, P²-Sp²—        and P³-Sp³— may denote a radical R^(aa), with the proviso that        at least one of the radicals P¹-Sp¹—, P²-Sp²— and P³-Sp³—        present does not denote R^(aa),-   R^(aa) denotes H, F, Cl, CN or straight-chain or branched alkyl    having 1 to 25 C atoms, wherein, in addition, one or more    non-adjacent CH₂ groups may each be replaced, independently of one    another, by    -   C(R⁰)═C(R⁰⁰)—, —C≡C—, —N(R⁰)—, —O—, —S—, —CO—, —CO—O—, —O—CO—,        —O—CO—O— in such a way that O and/or S atoms are not linked        directly to one another, and wherein, in addition, one or more H        atoms may be replaced by F, Cl, CN or P¹-Sp¹—, particularly        preferably straight-chain or branched, optionally mono- or        polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl,        alkoxycarbonyl or alkylcarbonyloxy having 1 to 12 C atoms (where        the alkenyl and alkynyl radicals have at least two C atoms and        the branched radicals have at least three C atoms),-   R⁰, R⁰⁰ each, independently of one another, denote H or alkyl having    1 to 12 C atoms,-   R^(y) and R^(z) each, independently of one another, denote H, F, CH₃    or CF₃,-   Z^(p1) denotes —O—, —CO—, —C(R^(y)R^(z))— or —CF₂CF₂—,-   Z^(p2) and Z^(p3) each, independently of one another, denote —CO—O—,    —O—CO—, —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂— or —(CH₂)_(n3)—, where n3 is    2, 3 or 4,-   L on each occurrence, identically or differently, denotes F, Cl, CN,    SCN, SF₅ or straight-chain or branched, optionally mono- or    polyfluorinated alkyl, alkoxy, alkenyl, alkynyl, alkylcarbonyl,    alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12    C atoms, preferably F,-   L′ and L″ each, independently of one another, denote H, F or Cl,-   r denotes 0, 1, 2, 3 or 4,-   s denotes 0, 1, 2 or 3,-   t denotes 0, 1 or 2, and-   x denotes 0 or 1.

In a particularly preferred embodiment of the present invention the LCmixture, or component C), comprises one or more compounds of formulaP10-1.

wherein the parameters are defined as described above and P¹ and P²preferably denote acrylate or methacrylate.

-   -   Particularly preferred compounds of formula P10-1 are selected        from the group of the following subformulae

wherein each n4 denote independently of each other an integer between 2and 10, preferably 3,4,5 or 6.

The polymerizable compounds of formulae I and P are also suitable forpolymerisation without an initiator, which is associated withconsiderable advantages, such as, for example, lower material costs and,in particular, reduced contamination of the LC medium by possibleresidual amounts of the initiator or degradation products thereof. Thepolymerisation can thus also be carried out without addition of aninitiator. The LC medium thus, in a preferred embodiment, comprises nopolymerisation initiator.

The polymerizable component C) or the LC medium as a whole may alsocomprise one or more stabilisers in order to prevent undesiredspontaneous polymerisation of the RMs, for example during storage ortransport. Suitable types and amounts of stabilisers are known to theperson skilled in the art and are described in the literature.Particularly suitable are, for example, the commercially availablestabilisers from the Irganox® series (BASF SE), such as, for example,Irganox® 1076. If stabilisers are employed, their proportion, based onthe total amount of the RMs or the polymerizable component, ispreferably 10-10,000 ppm, particularly preferably 50-1000 ppm.

The media according to the invention preferably comprise from 0.01 to10%, particularly preferably from 0.05 to 7.5% and most preferably from0.1 to 5% of the compounds of component C) comprising compounds offormula P according to the invention. The media preferably comprise one,two or three, more preferably one or two and most preferably onecompound of the formula P according to the invention.

By means of suitable additives, the liquid-crystalline phases of thepresent invention can be modified in such a way that they can be used inall types of liquid-crystal display element that have been disclosedhitherto. Additives of this type are known to the person skilled in theart and are described in detail in the literature (H. Kelker/R. Hatz,Handbook of Liquid Crystals, Verlag Chemie, Weinheim, 1980). Forexample, pleochroic dyes can be added for the production of colouredguest-host systems or substances can be added in order to modify thedielectric anisotropy, the viscosity and/or the alignment of the nematicphases.

The media according to the invention are prepared in a mannerconventional per se. In general, the components are dissolved in oneanother, preferably at elevated temperature.

Accordingly the present invention relates further to method for theproduction of an LC medium according to the present invention,comprising the step of mixing one or more compounds of formula I with aliquid-crystalline component B) comprising one or more mesogenic orliquid-crystalline compounds as described above.

The present invention further relates to a process for the fabricationof liquid crystal displays comprising at least the steps of:

-   -   providing a first substrate which includes a pixel electrode and        a common electrode for generating an electric field        substantially parallel to a surface of the first substrate in        the pixel region;    -   providing a second substrate, the second substrate being        disposed opposite to the first substrate;    -   interposing a liquid crystal mixture between the first substrate        and the second substrate, the liquid crystal mixture comprising        one or more compounds of formula I, component B) and optionally        component C);    -   irradiating the liquid crystal mixture with linearly polarised        light causing photoalignment of the liquid crystal;    -   curing the polymerizable compounds of the liquid crystal mixture        by irradiation with ultraviolet light or visible light having a        wavelength of 450 nm or below.

The present invention further relates to the use of the liquid crystalmixtures according to the invention for the fabrication of a liquidcrystal display.

The present invention further relates to liquid crystal displaysfabricated by the process described above.

In the following, the production process according to the presentinvention is described in greater detail.

The first substrate includes a pixel electrode and a common electrodefor generating an electric field substantially parallel to a surface ofthe first substrate in the pixel region. Various kinds of displayshaving at least two electrodes on one substrate are known to the skilledperson wherein the most significant difference is that either both thepixel electrode and the common electrode are structured, as it istypical for IPS displays, or only the pixel electrode is structured andthe common electrode is unstructured, which is the case for FFSdisplays.

It has to be understood that the present invention refers to any kind ofelectrode configurations suitable for generating an electric fieldsubstantially parallel to a surface of the first substrate in the pixelregion; mentioned above, i.e. IPS as well as FFS displays.

The process according to the present invention is independent of thekind of substrate or material of the surface which is in contact withthe liquid crystal mixture according to the invention, during and afterthis process. Examples of materials used for the substrates or surfacesare organic polymers including polyimide, indium tin oxide (ITO), indiumzinc oxide (IZO), silicon nitride (SiN_(x)) and silicon dioxide (SiO₂).The process is especially suitable for the use in displays containingsubstrates that do not have a polyimide layer on one or more of thesurfaces that are in contact with the liquid crystal.

In case one or more substrates contain a polyimide layer, the polyimidecan be rubbed or not rubbed, preferably not rubbed.

Hence, the invention relates to a display produced by the processaccording to the invention in which the substrates contain a rubbed orunrubbed polyimide layer, preferably an unrubbed polyimide layer.

The invention further relates to a display produced by the processaccording to the invention in which none or only one of the top andbottom substrates contains a polyimide layer.

In one embodiment of the present invention the liquid crystalcomposition is injected between the first and second substrates or isfilled into the cell by capillary force after combining the first andsecond substrates. In an alternative embodiment, the liquid crystalcomposition may be interposed between the first and second substrates bycombining the second substrate to the first substrate after loading theliquid crystal composition on the first substrate. Preferably, theliquid crystal is dispensed dropwise onto a first substrate in a processknown as “one drop filling” (ODF) process, as disclosed in for exampleJPS63-179323 and JPH10-239694, or using the Ink Jet Printing (IJP)method.

In a preferred embodiment, the process according to the inventioncontains a process step where the liquid crystal inside the displaypanel is allowed to rest for a period of time in order to evenlyredistribute the liquid crystal medium inside the panel (herein referredto as “annealing”).

However it is likewise preferred that the annealing step is combinedwith a previous step, such as edge sealant pre-curing. In which case a‘separate’ annealing step may not be necessary at all.

For the production of the displays according to the present invention,the photoreactive mesogen of formula I is preferably allowed toredistribute in the panel. After filling and assembly, the display panelis annealed for a time between 1 min and 3 h, preferably between 2 minand 1 h and most preferably between 5 min and 30 min. The annealing ispreferably performed at room temperature.

In an alternative embodiment, the annealing is performed at elevatedtemperature, preferably at above 20° C. and below 140° C., morepreferably above 40° C. and below 100° C. and most preferably above 50°C. and below 80° C.

In a preferred embodiment, one or more of the process steps of fillingthe display, annealing, photoalignment and curing of the polymerizablecompound is performed at a temperature above the clearing point of theliquid crystal host mixture.

During the photoalignment of the liquid crystal inside the liquidcrystal panel, anisotropy is induced by exposing the display or theliquid crystal layer to linearly polarised light.

In a preferred embodiment of the present invention the photoreactivecomponent A) comprising one or more compounds of formula I, isphotoaligned in a first step using linearly polarised light and in asecond step further cured using linearly polarized or unpolarised UVlight. In the second step the optional component C) is also furthercured.

In another preferred embodiment, the linearly polarised light appliedaccording to the inventive process is ultraviolet light which enablessimultaneous photoalignment and photocuring of the photoreactivecomponent A) comprising one or more compounds of formula I, and, ifpresent, photocuring of the polymerizable component C).

Photoalignment of the photoreactive compounds of formula I and curing ofthe polymerizable groups of compounds of formula I and the curing of theoptional polymerizable compounds of formula P can be performedsimultaneously or stepwise. In case the process is split into differentsteps, the individual steps can be performed at the same temperature orat different temperatures.

After the photoalignment and curing step(s) a so-called “post-curing”step can optionally be performed by irradiation with UV-light and/orvisible light (both either linearly or unpolarised) at reducedtemperature in order to remove unreacted polymerizable compounds. Thepost-curing is preferably performed at above 0° C. and below theclearing point of the utilized LC mixture, preferably 20° C. and below60° C.° C., and most preferably above 20° C. and below 40° C.

The polymerizable compounds are optionally polymerised or crosslinked(if a polymerizable compound contains two or more polymerizable groups)with the application of an electrical field. The polymerisation can becarried out in one or more steps.

Suitable and preferred polymerisation methods for component C) are, forexample, thermal or photopolymerization, preferably photopolymerization,in particular UV photopolymerization. One or more initiators canoptionally also be added here. Suitable conditions for thepolymerisation and suitable types and amounts of initiators are known tothe person skilled in the art and are described in the literature.Suitable for free-radical polymerisation are, for example, thecommercially available photoinitiators Irgacure651®, Irgacure184®,Irgacure907®, Irgacure369® or Darocure1173® (BASF SE). If an initiatoris employed, its proportion is preferably 0.001 to 5% by weight,particularly preferably 0.001 to 1% by weight.

The present invention also relates to electro-optical liquid-crystaldisplay elements containing a liquid-crystalline medium according to theinvention, which is preferably homogeneously aligned. In a preferredembodiment the liquid crystal display is of the IPS or FFS mode.

Further combinations of the embodiments and variants of the invention inaccordance with the description arise from the claims.

The invention is explained in greater detail below with reference toworking examples, but without intending to be restricted thereby. Theperson skilled in the art will be able to glean from the examplesworking details that are not given in detail in the general description,generalise them in accordance with general expert knowledge and applythem to a specific problem.

Besides the usual and well-known abbreviations, the followingabbreviations are used:

C: crystalline phase; N: nematic phase; Sm: smectic phase; I: isotropicphase. The numbers between these symbols show the transitiontemperatures of the substance concerned.

Temperature data are in ° C., unless indicated otherwise.

Physical, physicochemical or electro-optical parameters are determinedby generally known methods, as described, inter alia, in the brochure“Merck Liquid Crystals—Licristal®—Physical Properties of LiquidCrystals—Description of the Measurement Methods”, 1998, Merck KGaA,Darmstadt.

Above and below, Δn denotes the optical anisotropy (589 nm, 20° C.) andΔε denotes the dielectric anisotropy (1 kHz, 20° C.). The dielectricanisotropy Δε is determined at 20° C. and 1 kHz. The optical anisotropyΔn is determined at 20° C. and a wavelength of 589.3 nm.

The Δε and Δn values and the rotational viscosity (γ₁) of the compoundsaccording to the invention are obtained by linear extrapolation fromliquid-crystalline mixtures consisting of 5 to 10% of the respectivecompound according to the invention and 90-95% of the commerciallyavailable liquid-crystal mixture ZLI-2857 (for Δε) or ZLI-4792 (for Δn,γ₁) (mixtures, Merck KGaA, Darmstadt).

The compounds used in the present invention are prepared by methodsknown per se, as described in the literature (for example in thestandard works, such as Houben-Weyl, Methoden der organischen Chemie[Methods of Organic Chemistry], Georg-Thieme-Verlag, Stuttgart), to beprecise under reaction conditions which are known and suitable for thesaid reactions. Use can also be made here of variants known per se,which are not mentioned here in greater detail.

In the present invention and especially in the following examples, thestructures of the mesogenic compounds are indicated by means ofabbreviations, also called acronyms. In these acronyms, the chemicalformulae are abbreviated as follows using Tables A to C below. Allgroups C_(n)H_(2n+1), C_(m)H_(2m+1) and C₁H_(2l+1) or C_(n)H_(2n−1),C_(m)H_(2m−1) and C₁H_(2l−1) denote straight-chain alkyl or alkenyl,preferably 1E-alkenyl, each having n, m and l C atoms respectively.Table A lists the codes used for the ring elements of the corestructures of the compounds, while Table B shows the linking groups.Table C gives the meanings of the codes for the left-hand or right-handend groups. The acronyms are composed of the codes for the ring elementswith optional linking groups, followed by a first hyphen and the codesfor the left-hand end group, and a second hyphen and the codes for theright-hand end group. Table D shows illustrative structures of compoundstogether with their respective abbreviations.

TABLE A Ring elements

C

P

D

DI

A

AI

G

GI

U

UI

Y

M

MI

N

NI

Np

dH

N3f

N3fl

tH

tHI

tH2f

tH2fl

K

KI

L

LI

F

FI

Nf

Nfl

TABLE B Linking groups E —CH₂CH₂— Z —CO—O— V —CH═CH— ZI —O—CO— X —CF═CH—O —CH₂—O— XI —CH═CF— OI —O—CH₂— B —CF═CF— Q —CF₂—O— T —C≡C— QI —O—CF₂— W—CF₂CF₂— T —C≡O—

TABLE C End groups Left-hand side Right-hand side Use alone -n-C_(n)H_(2n+1)— -n —C_(n)H_(2n+1) —nO— C_(n)H_(2n+1)—O— —nO—O—C_(n)H_(2n+1) —V— CH₂═CH— —V —CH═CH₂ —nV— C_(n)H_(2n+1)—CH═CH— —nV—C_(n)H_(2n)—CH═CH₂ —Vn— CH₂═CH—C_(n)H_(2n+1)— —Vn —CH═CH—C_(n)H_(2n+1)—nVm— C_(n)H_(2n+1)—CH═CH—C_(m)H_(2m)— —nVm—C_(n)H_(2n)—CH═CH—C_(m)H_(2m+1) —N— N≡C— —N —C≡N —S— S═C═N— —S —N═C═S—F— F— —F —F —CL— Cl— —CL —Cl —M— CFH₂— —M —CFH₂ —D— CF₂H— —D —CF₂H —T—CF₃— —T —CF₃ —MO— CFH₂O— —OM —OCFH₂ —DO— CF₂HO— —OD —OCF₂H —TO— CF₃O——OT —OCF₃ —FXO— CF₂═CH—O— —OXF —O—CH═CF₂ —A— H—C≡C— —A —C≡C—H —nA—C_(n)H_(2n+1)—C≡C— —An —C≡C—C_(n)H_(2n+1) —NA— N≡C—C≡C— —AN —C≡C—C≡N Usetogether with one another and with others — . . . A . . . — —C≡— — . . .A . . . —C≡— — . . . V . . . — CH═CH— — . . . V . . . —CH═CH— — . . . Z. . . — —CO—O— — . . . Z . . . —CO—O— — . . . ZI . . . — —O—CO— — . . .ZI . . . —O—CO— — . . . K . . . — —CO— — . . . K . . . —CO— — . . . W .. . — —CF═CF— — . . . W . . . —CF═CF—wherein n and m each denote integers, and the three dots “ . . . ” areplaceholders for other abbreviations from this table.

The following table shows illustrative structures together with theirrespective abbreviations. These are shown in order to illustrate themeaning of the rules for the abbreviations. They furthermore representcompounds which are preferably used.

TABLE D Illustrative structures

CC-n-m

CC-n-Om

CC-n-V

CC-n-Vm

CC-n-mV

CC-n-mVI

CC-V-V

CC-V-mV

CC-V-Vm

CC-Vn-mV

CC-nV-mV

CC-nV-Vm

CP-n-m

CP-nO-m

CP-n-Om

CP-V-m

CP-Vn-m

CP-nV-m

CP-V-V

CP-V-mV

CP-V-Vm

CP-Vn-mV

CP-nV-mV

CP-nV-Vm

PP-n-m

PP-nO-m

PP-n-Om

PP-n-V

PP-n-Vm

PP-n-mV

PP-n-mVI

CCP-n-m

CCP-nO-m

CCP-n-Om

CCP-n-V

CCP-n-Vm

CCP-n-mV

CCP-n-mVI

CCP-V-m

CCP-nV-m

CCP-Vn-m

CCP-nVm-I

CPP-n-m

CPG-n-m

CGP-n-m

CPP-nO-m

CPP-n-Om

CPP-V-m

CPP-nV-m

CPP-Vn-m

CPP-nVm-I

PGP-n-m

PGP-n-V

PGP-n-Vm

PGP-n-mV

PGP-n-mVI

CCEC-n-m

CCEC-n-Om

CCEP-n-m

CCEP-n-Om

CPPC-n-m

CGPC-n-m

CCPC-n-m

CCZPC-n-m

CPGP-n-m

CPGP-n-mV

CPGP-n-mVI

PGIGP-n-m

CP-n-F

CP-n-CL

GP-n-F

GP-n-CL

CCP-n-OT

CCG-n-OT

CCP-n-T

CCG-n-F

CCG-V-F

CCG-V-F

CCU-n-F

CDU-n-F

CPG-n-F

CPU-n-F

CGU-n-F

PGU-n-F

GGP-n-F

GGP-n-CL

PGIGI-n-F

PGIGI-n-CL

CCPU-n-F

CCGU-n-F

CPGU-n-F

CPGU-n-OT

DPGU-n-F

PPGU-n-F

CCZU-n-F

CCQP-n-F

CCQG-n-F

CCQU-n-F

PPQG-n-F

PPQU-n-F

PGQU-n-F

GGQU-n-F

PUQU-n-F

MUQU-n-F

NUQU-n-F

CDUQU-n-F

CPUQU-n-F

CGUQU-n-F

PGPQP-n-F

PGPQG-n-F

PGPQU-n-F

PGUQU-n-F

APUQU-n-F

DGUQU-n-F

CY-n-Om

CY-n-m

CY-V-Om

CY-nV-(O)m

CVC-n-m

CVY-V-m

CEY-V-m

PY-n-(O)m

CCY-n-m

CCY-n-Om

CCY-V-m

CCY-Vn-m

CCY-V-Om

CCY-n-OmV

CCY-n-zOm

CCOC-n-m

CPY-n-(O)m

CPY-V-Om

CQY-n-(O)m

CQIY-n-(O)m

CCQY-n-(O)m

CCQIY-n-(O)m

CPQY-n-(O)m

CPQIY-n-Om

CLY-n-(O)m

CYLI-n-m

LYLI-n-m

LY-n-(O)m

PGIGI-n-F

PGP-n-m

PYP-n-(O)m

PYP-n-mV

YPY-n-m

YPY-n-mV

BCH-nm

BCH-nmF

CPYP-n-(O)m

CPGP-n-m

CPYC-n-m

CYYC-n-m

CCYY-n-m

CPYG-n-(O)m

CBC-nm

CBC-nmF

CNap-n-Om

CCNap-n-Om

CENap-n-Om

CTNap-n-Om

CETNap-n-Om

CK-n-F

DFDBC-n(O)-(O)m

C-DFDBF-n-(O)mwherein n, m and l preferably, independently of one another, denote 1 to7.

The following table, Table E, shows illustrative compounds which can beused as additional stabilisers in the mesogenic media according to thepresent invention.

TABLE E Table E shows possible stabilisers which can be added to the LCmedia according to the invention. (n here denotes an integer from 1 to12, preferably 1, 2, 3, 4, 5, 6, 7 or 8, terminal methyl groups are notshown).

The LC media preferably comprise 0 to 10% by weight, in particular 1 ppmto 5% by weight, particularly preferably 1 ppm to 1% by weight, ofstabilisers.

Table F below shows illustrative compounds which can preferably be usedas chiral dopants in the mesogenic media according to the presentinvention.

TABLE F

In a preferred embodiment of the present invention, the mesogenic mediacomprise one or more compounds selected from the group of the compoundsfrom Table F.

The mesogenic media according to the present application preferablycomprise two or more, preferably four or more, compounds selected fromthe group consisting of the compounds from the above tables.

The liquid-crystal media according to the present invention preferablycomprise

-   -   seven or more, preferably eight or more, individual compounds,        preferably of three or more, particularly preferably of four or        more, different formulae, selected from the group of the        compounds from Table D.

Hereinafter, the present invention is described in more detail andspecifically with reference to the Examples, which however are notintended to limit the present invention.

EXAMPLES Compound Examples 1.1 Synthesis of diethyl3-(2-benzyloxyethyl)pentanedioate (1)

Under reflux 13.8 ml (90 mmol) of the diethyl malonate are added tomixture of 34.5 ml of a solution of sodium methylate in ethanol (20%, 50mmol) and 40 ml ethanol. After 2h 10 g (50 mmol) of2-bromoethoxymethylbenzene are added and heating was continuedovernight. Water and MTB ether are poured into the cooled reactionmixture. The aqueous layer is extracted with MTB ether. The combinedorganic layers are washed with brine and dried over sodium sulfate. Thesolvent is evaporated. The residue is purified by silica chromatography(toluene; toluene/MTB ether 9:1). The isolated material is distilledunder vacuum (0.1 mbar, 116-121° C.).

1.2 Synthesis of 2-(2-benzyloxyethyl)propane-1,3-diol (2)

A solution of 5 g (20 mmol) of the malonate 1 in 60 ml toluene is addedto a suspension of 930 mg (24 mmol) Lithium aluminum hydride in 8 mlToluene. After 3h reflux the cooled reaction mixture is quenched withethyl acetate. The mixture is acidified with 2 mol/l hydrochloric acid(pH 3-4). The aqueous layer is extracted with MTB ether. The combinedorganic layers are washed with water and dried over sodium sulfate. Thesolvent is evaporated. The residue is purified by silica chromatography(ethyl acetate.

1.3 Synthesis of[4-benzyloxy-2-[[tert-butyl(dimethyl)silyl]oxymethyl]butoxy]-tert-butyl-dimethyl-silane(3)

At room temperature 3.4 ml (25 mmol) triethyl amine are added to amixture of 2.1 g (10 mmol) of the diol 2 and 120 mg DMAP dissolved in 30ml dichloro methane. Afterwards a solution of 4.5 g (30 mmol) TBDMS-Clin 15 ml dichloro methane are added to the reaction mixture at 3-4° C.After stirring 16h at room temperature the mixture is quenched withwater. The combined organic layers are washed with brine and dried oversodium sulfate. The solvent is evaporated. The residue is purified bysilica chromatography (n-heptane/ethyl acetate 19:1).

1.4 Synthesis of4-[tert-butyl(dimethyl)silyl]oxy-3-[[tert-butyl(dimethyl)silyl]oxy-methyl]-butan-1-ol(4)

A solution of 500 mg (1 mmol) of 3 in 13 ml ethyl acetate ishydrogenated using Pd/C-5% at room temperature. The solvent isevaporated. The residue is purified by silica chromatography(n-heptane/ethyl acetate (gradient)).

1.5 Synthesis of[4-[(6-bromo-2-naphthyl)oxy]-2-[[tert-butyl(dimethyl)silyl]oxymethyl]butoxy]-tert-butyl-dimethyl-silane(5)

A solution of 10 g (43 mmol) 2-hydroxy-6-bromo naphthalene, 17.1 g (49mmol) 5 and 13.1 g triphenylphosphine in 80 ml THF is treated with 10.2ml (52 mmol) diisopropyl carboxylate at room temperature. The mixture isstirred overnight. The solvent is evaporated. The residue is purified bysilica chromatography (toluene).

1.6 Synthesis of butyl(E)-3-[6-[4-[tert-butyl(dimethyl)silyl]oxy-3-[[tert-butyl(dimethyl)silyl]oxymethyl]butoxy]-2-naphthyl]prop-2-enoate(6)

A solution of 24.8 g (84% pure, 38 mmol) 5, 6.4 ml (45 mmol) butylacrylate and 10.5 ml triethyl amine in 150 ml acetonitrile is treatedwith 250 mg Palladium(II)acetate and 570 mg tri-(o-tolyl) phosphine andrefluxed overnight. The solvent is evaporated. The residue is filtratedthrough silica gel (n-heptane/toluene 1:1; toluene).

1.7 Synthesis of(E)-3-[6-[4-[tert-butyl(dimethyl)silyl]oxy-3-[[tert-butyl(dimethyl)silyl]oxymethyl]butoxy]-2-naphthyl]prop-2-enoicacid (7)

A solution of 20.5 g (33 mmol) 6 in 100 ml THF and 16 ml methanol istreated with 34 ml 2N sodium hydroxide and stirred at 30° C. overnight.The mixture is added to 1.5 l aqueous saturated ammonia hydrochloridesolution and acidified with 1N hydrochloric acid (pH 5). The aqueouslayer is extracted with MTB ether. The organic layer is dried withsodium sulfate. The solvent is evaporated. The residue is dried underlow pressure.

1.8 Synthesis of 1-[4-(benzyloxy)-3-methylphenyl]ethan-1-one 8

12.7 g (85.0 mmol) of 1-(4-hydroxy-3-methyl-phenyl)-ethanone, 12.7 mL(107 mmol) benzyl bromide and 7.62 g (55.0 mmol) potassium carbonate aredissolved/suspended in methyl(ethyl)ketone and stirred for 18 h underreflux. The reaction mixture is cooled down to room temperature (RT) andthe precipitating solid is filtered and washed with methyltertiary-butyl ether (MTB-E). The product is further crystallized out ofheptane at 5° C. and is directly used in the next synthesis step.

1.9 Synthesis of 4-(benzyloxy)-3-methylphenyl acetate 9

39.1 mL (0.165 mmol) m-chloroperbenzoic acid are suspended in in 102 mLmethylene chloride and a solution of 19.3 g (80.0 mmol) of ketone 8 in72 mL methylene chloride is added dropwise to the reaction mixture. Theyellow reaction mixture is then stepwise heated up to reflux and stirredfor 16 h. The reaction mixture is cooled to room temperature (RT) andpoured onto ice water. The phases are separated and the organic layer isfiltered off from precipitated 3-chlorobenzoic acid, washed with sodiumhydrogen carbonate, tested for peroxide remnants (with ammonia iron(II)sulfate solution), dried over sodium sulfate, filtered and evaporatedunder vacuum. The crude product is filtered through 900 g silica gelwith toluene and ethyl acetate (95:5) to give the product as a yellowoil.

1.10 Synthesis of 4-(benzyloxy)-3-methylphenol 10

23.4 g (91.0 mmol) acetate 9 are solved in 181.0 mL ethanol and 5.84 mL(197.0 mmol) sodium hydroxide solution (32%) are added dropwise to thesolution (the reaction solution turned to red color). The reactionmixture is stirred for 2h at ambient temperature and then poured ontoice water and treated with HCl solution till a pH value of 1 isachieved. The reaction mixture is extracted with methyl tertiary-butylether (MTB-E), the organic layer dried over sodium sulfate, filtered andevaporated under vacuum. The black oil is filtered over silica gel withmethylene chloride and the obtained solid is then crystallized out ofheptane at −25° C. to give slightly brown colored crystals.

¹H NMR (500 MHz, DMSO-d6)

δ=2.13 ppm (s, 3H, CH₃), 4.99 (s, 2H, CH₂—O), 6.51 (dd, J=2.86, 8.62 Hz,1H), 6.58 (d, J=2.49 Hz, 1H), 6.81 (d, J=8.70 Hz, 1H), 7.32 (d, J=7.23Hz, 1H), 7.39 (t, J=7.71 Hz, 2H), 7.44 (d, J=8.70 Hz, 2H).

1.11 Synthesis of benzyl 4-triisopropylsilyloxybenzoate (11)

A mixture of 400 ml DMF, 75 g (328 mmol) benzyl-4-hydroxybenzoate and 45g (661 mmol) imidazole was treated with a solution of 77.5 ml (361 mmol)chloro triisopropyl silane in 200 ml DMF at room temperature. After 5hstirring the reaction mixture is diluted with toluene and n-heptane andpoured ice cold water. The aqueous layer is extracted with toluene, thecombined organic layers are dried with sodium sulfate and filtratedthrough silica gel (n-heptane/toluene 1:1). The solvent of the productcontaining fractions is evaporated. Yield: 116 g 11

1.12 Synthesis of 4-triisopropylsilyloxybenzoic acid (12)

A solution of 116 g (296 mmol) 11 in ethanol is hydrogenated with Pd-C5%(51.4% water) at room temperature. The reaction mixture is diluted withMTB ether. Silica gel and Celite® are added. The obtained mixture isfiltrated through silica gel/Celite® (MTB ether). The solvent of theproduct containing fraction is evaporated. The residue is crystallizedfrom n-heptane (6° C.).

1.13 Synthesis of (4-benzyloxy-3-methyl-phenyl)4-triisopropylsilyloxybenzoate (13)

A solution of 21.1 g (98 mmol) 10 and 29 g (98 mmol) 12 in 900 mldichloro methane is treated with 600 mg DMAP and 22.6 g (118 mmol)N-(3-dimethylamino propyl)-N′-ethyl carbodiimide hydrochloride andstirred overnight at room temperature. The mixture was filtered throughsilica gel (dichloromethane). The solvent of the product containingfraction is evaporated.

1.14 Synthesis of (4-hydroxy-3-methyl-phenyl)4-triisopropylsilyloxybenzoate (14)

A solution of 35 g (71 mmol) 13 in 350 ml THF is hydrogenated withPd-C5% (51.4% water) at room temperature. The solvent is evaporated.

1.15 Synthesis of[4-[(E)-3-[6-[4-[tert-butyl(dimethyl)silyl]oxy-3-[[tert-butyl(dimethyl)silyl]oxymethyl]butoxy]-2-naphthyl]prop-2-enoyl]oxy-3-methyl-phenyl]4-triisopropylsilyloxybenzoate (15)

A solution of 3.9 g (6.9 mmol) 7 and 2.7 g (6.7 mmol) 14 in 40 mldichloro methane is treated with 40 mg DMAP and 1.5 g (7.8 mmol)N-(3-dimethylamino propyl)-N′-ethyl carbodiimide hydrochloride andstirred overnight at room temperature. The mixture was filtered throughsilica gel (dichloro methane). The solvent of the product containingfraction is evaporated. Yield 5.4 g 15

1.18 Synthesis of[4-[(E)-3-[6-[4-hydroxy-3-(hydroxymethyl)butoxy]-2-naphthyl]prop-2-enoyl]oxy-3-methyl-phenyl]4-hydroxybenzoate (16)

A solution of 4.9 g (5.3 mmol) 15 in 60 ml THF is treated with 6.5 ml(40 mmol) triethylamine trishydrofluoride at a temperature below 5° C.The reaction mixture is stirred overnight at room temperature, andfiltered through silica gel collecting fractions (THF). The productcontaining fraction are combined and the solvent is evaporated. Theresidue is suspended in 12 ml acetonitrile and heated to reflux. Themixture is cooled to 6° C. The precipitate is isolated.

1.17 Synthesis of[3-methyl-4-[(E)-3-[6-[4-(2-methylprop-2-enoyloxy)-3-(2-methylprop-2-enoyloxymethyl)butoxy]-2-naphthyl]prop-2-enoyl]oxy-phenyl]4-(2-methylprop-2-enoyloxy)benzoate (17)

A mixture of 1.3 g (2.4 mmol) 16 and 15 ml dichloro methane is treatedwith 1.0 ml (12 mmol) methacrylic acid and 30 mg DMAP. At 5° C. 2.4 ml(14 mmol) N-(3-dimethylamino propyl)-N′-ethyl are added. After 1 hstirring at this temperature stirring is continued at room temperatureovernight. The reaction mixture is purified by silica chromatography(dichloro methane/THF gradient 2%). Further purification bychromatography on reversed phase silica gel (acetonitrile) andcrystallization from acetonitrile.

¹H NMR (700 MHz, Chloroform-d) δ=8.25 (d, J=8.4 Hz, 2H), 8.03 (d, J=15.9Hz, 1H), 7.94 (s, 1H), 7.78 (d, J=8.9 Hz, 1H), 7.77-7.70 (m, 2H), 7.29(d, J=8.6 Hz, 2H), 7.19-7.08 (m, 5H), 6.73 (d, J=15.9 Hz, 1H), 6.40 (s,1H), 6.12 (s, 2H), 5.85-5.79 (m, 1H), 5.60-5.54 (m, 2H), 4.30 (d, J=5.7Hz, 4H), 4.23 (t, J=6.2 Hz, 2H), 2.51 (p, J=6.2 Hz, 1H), 2.27 (s, 3H),2.09 (s, 3H), 2.02 (q, J=6.4 Hz, 2H), 1.95 (s, 6H).

In accordance or in analogy to the above described procedures, thefollowing compounds are obtained:

No. Structure RM-1

RM-2

RM-3

RM-4

RM-5

Comparative Compounds

Nematic Host Mixtures

The nematic LC host mixture are prepared as indicated in the followingtables:

Mixture N—1:

Composition [%-w/w] Physical properties CC-3-V 36.00 Clearing Point [°C.]: 78 CC-3-V1 5.00 n_(e) [589 nm, 20° C.]: 1.5907 CCP-V-1 8.00 Δn [589nm, 20° C.]: 0.1095 PGP-2-2V 3.00 ε_(∥) [1 kHz, 20° C.]: 16.6 CCQU-3-F9.5 ε_(⊥) [1 kHz, 20° C.]: 3.7 PUQU-3-F 8.5 Δε [1 kHz, 20° C.]: 12.9APUQU-2-F 5.00 K₁ [pN, 20° C.]: 12.1 APUQU-3-F 8.00 K₃ [pN, 20° C.]:13.4 PGUQU-3-F 4.00 K₃/K₁ [pN, 20° C.]: 1.11 PGUQU-4-F 8.00 V₀ [V, 20°C.]: 1.01 PGUQU-5-F 5.00 LTS bulk [h, −20° C.]: 1000 Σ 100.0Mixture N—2:

Composition [%-w/w] Physical properties CC-3-V 44.00 Clearing Point [°C.]: 80.5 CC-3-V1 12.00 n_(e) [589 nm, 20° C.]: 1.5865 CCP-V-1 11.00 Δn[589 nm, 20° C.]: 0.0991 CCP-V2-1 9.00 ε_(∥) [1 kHz, 20° C.]: 5.3PGP-2-3 6.00 ε_(⊥) [1 kHz, 20° C.]: 2.6 PGUQU-3-F 6.00 Δε [1 kHz, 20°C.]: 2.7 APUQU-3-F 4.5 K₁ [pN, 20° C.]: 14.6 PP-1-2V1 7.00 K₃ [pN, 20°C.]: 15.9 PPGU-3-F 0.5 K₃/K₁ [pN, 20° C.]: 1.09 Σ 100.0 V₀ [V, 20° C.]:2.46 LTS bulk [h, −20° C.]: 1000Mixture N—3:

Composition [%-w/w] Physical properties CY-3-O2 12.00 Clearing Point [°C.]: 85.2 CY-5-O2 10.5 n_(e) [589 nm, 20° C.]: 1.5956 CCY-3-O1 6.00 Δn[589 nm, 20° C.]: 0.1120 CCY-3-O2 7.00 ε_(∥) [1 kHz, 20° C.]: 3.7CCY-5-O2 5.00 ε_(⊥) [1 kHz, 20° C.]: 7.9 CPY-2-O2 12.00 Δε [1 kHz, 20°C.]: −4.2 CPY-3-O2 12.00 PYP-2-3 7.5 CC-3-V1 4.00 CC-3-V 24.00 Σ 100.0Mixture N—4:

Composition [%-w/w] Physical properties CC-3-V 50.00 Clearing Point [°C.]: 79.4 CC-3-V1 4.5 n_(e) [589 nm, 20° C.]: 1.5981 CCP-V-1 13.5 Δn[589 nm, 20° C.]: 0.1094 CPGU-3-OT 6.00 ε_(∥) [1 kHz, 20° C.]: 8.1PGP-2-2V 6.5 ε_(⊥) [1 kHz, 20° C.]: 2.9 PGU-2-F 10.00 Δε [1 kHz, 20°C.]: 5.2 PGUQU-3-F 7.00 K₁ [pN, 20° C.]: 12.6 PPGU-3-F 1.00 K₃ [pN, 20°C.]: 14.2 PUQU-2-F 1.5 K₃/K₁ [pN, 20° C.]: 1.13 Σ 100.0 V₀ [V, 20° C.]:1.64 LTS bulk [h, −20° C.]: 240Mixture N—5:

Composition [%-w/w] Physical properties CC-3-V 30.00 Clearing Point [°C.]: 87 CC-3-V1 10.00 n_(e) [589 nm, 20° C.]: 1.5829 CCH-34 2.5 Δn [589nm, 20° C.]: 0.1019 CCP-V-1 1.5 ε_(∥) [1 kHz, 20° C.]: 3.5 PGIY-2-O44.00 ε_(⊥) [1 kHz, 20° C.]: 7.1 CCY-3-O2 10.00 Δε [1 kHz, 20° C.]: −3.7CCY-5-O2 2.00 K₁ [pN, 20° C.]: 15.2 CLY-3-O2 8.00 K₃ [pN, 20° C.]: 18.0CPY-2-O2 6.00 K₃/K₁ [pN, 20° C.]: 1.19 CPY-3-O2 10.00 V₀ [V, 20° C.]:2.35 CY-3-O2 12.00 LTS bulk [h, −20° C.]: 0 B-2O-O5 4.00 Σ 100.0Mixture N—6:

Composition [%-w/w] Physical properties CC-3-V 21.75 Clearing Point [°C.]: 91 CC-3-V1 10.45 n_(e) [589 nm, 20° C.]: 1.5970 CPP-V-3 9.52 n_(o)[589 nm, 20° C.]: 1.4865 BCH-32 4.74 Δn [589 nm, 20° C.]: 0.1105 BCH-523.55 ε_(∥) [1 kHz, 20° C.]: 3.8 PYP-2-3 9.76 ε_(⊥) [1 kHz, 20° C.]: 8.1COY-3-O1 3.19 Δε [1 kHz, 20° C.]: −4.3 COY-3-O2 6.53 K₁ [pN, 20° C.]:15.8 COY-1V-O2 3.22 K₃ [pN, 20° C.]: 19.0 CCOY-3-O2 8.74 K₃/K₁ [pN, 20°C.]: 1.20 CCOY-2-O2 8.89 V₀ [V, 20° C.]: 2.21 CCOY-V-O2 2.67 CCOY-V-O32.64 CCOY-1V-O2 4.35 Σ 100.0Mixture N—7:

Composition [%-w/w] Physical properties CC-3-V 29.0 Clearing Point [°C.]: 70 CC-3-V1 10.0 n_(e) [589 nm, 20° C.]: 1.5976 CCP-V-1 12.0 n_(o)[589 nm, 20° C.]: 1.4894 CCP-V2-1 4.0 Δn [589 nm, 20° C.]: 0.1082CCY-V-O2 8.0 ε_(∥) [1 kHz, 20° C.]: 3.4 COY-3-O2 2.0 ε_(⊥) [1 kHz, 20°C.]: 5.5 CCOY-3-O2 4.0 Δε [1 kHz, 20° C.]: −2.2 PY-3-O2 8.0 K₁ [pN, 20°C.]: 12.7 PY-V2-O2 14.0 K₃ [pN, 20° C.]: 14.5 PYP-2-3 9.0 K₃/K₁ [pN, 20°C.]: 1.14 Σ 100.0 V₀ [V, 20° C.]: 2.73 γ₁ [mPa s, 20° C.]: 66 LTS bulk[h, −20° C.]: 0Mixture N—8:

Composition [%-w/w] Physical properties CC-3-V 29.0 Clearing Point [°C.]: 70.5 CC-3-V1 9.0 n_(e) [589 nm, 20° C.]: 1.5976 CCP-V-1 13.0 n_(o)[589 nm, 20° C.]: 1.4889 CCY-V-O2 10.0 Δn [589 nm, 20° C.]: 0.1087COY-3-O2 2.0 ε_(∥) [1 kHz, 20° C.]: 3.5 CCOY-3-O2 6.0 ε_(⊥) [1 kHz, 20°C.]: 6.0 PY-3-O2 8.0 Δε [1 kHz, 20° C.]: −2.5 PY-V2-O2 14.0 K₁ [pN, 20°C.]: 12.6 PYP-2-3 9.0 K₃ [pN, 20° C.]: 14.6 Σ 100.0 K₃/K₁ [pN, 20° C.]:1.16 V₀ [V, 20° C.]: 2.55 γ₁ [mPa s, 20° C.]: 70 LTS bulk [h, −20° C.]:96Mixture N—9:

Composition [%-w/w] Physical properties CC-3-V 29.0 Clearing Point [°C.]: 81 PP-1-3 2.0 n_(e) [589 nm, 20° C.]: 1.5909 CC-3-V1 4.0 n_(o) [589nm, 20° C.]: 1.4840 CEY-3-O2 4.0 Δn [589 nm, 20° C.]: 0.1069 COY-3-O27.0 ε_(∥) [1 kHz, 20° C.]: 3.8 CAIY-3-O2 10.0 ε_(⊥) [1 kHz, 20° C.]: 8.4PYP-2-3 17.0 Δε [1 kHz, 20° C.]: −4.6 CCOY-2-O2 16.0 K₁ [pN, 20° C.]:14.4 CCOY-3-O2 11.0 K₃ [pN, 20° C.]: 16.8 Σ 100.0 K₃/K₁ [pN, 20° C.]:1.17 V₀ [V, 20° C.]: 2.03 γ₁ [mPa s, 20° C.]: 134 LTS bulk [h, −20° C.]:264

Fabrication of Display Cells

Unless explicitly stated otherwise, the display cells are made withCorning AF glass of 0.7 mm thickness using 6.4 μm spacer beads andXN-1500T sealant.

For measurement of electro-optics 3 μm thick PI-free IPS cells are madeof substrates commercially available from SD-tech and constructed intocells using ITO electrodes having 5 μm electrode spacing and a 3 μmelectrode width.

The cells are assembled by hand and then cured using a Omnicure 2000Mercury lamp with with 35 mW/cm² the irradiation power is therebymeasured by an Opsytec UV pad-e spectroradiometer.

Mixture Examples

Nematic LC mixtures M-1 to M-24 according to the invention are preparedfrom the nematic host mixtures N-1 to N-9 listed above andphotoalignment additives of formula I, according to the compositionsgiven in the following table.

c [%] of Photoalignment Mixture Host Host additive example MixtureMixture Compound c [%] M-1 N-1 99.70 RM-1 0.30 M-2 N-1 99.50 RM-1 0.50M-3 N-1 99.00 RM-1 1.00 M-4 N-1 99.50 RM-2 0.50 M-5 N-1 99.00 RM-2 1.00M-6 N-1 99.70 RM-3 0.30 M-7 N-1 99.50 RM-3 0.50 M-8 N-1 99.00 RM-3 1.00M-9 N-2 99.50 RM-2 0.50 M-10 N-2 99.00 RM-2 1.00 M-11 N-3 99.50 RM-20.50 M-12 N-3 99.00 RM-2 1.00 M-13 N-4 99.50 RM-2 0.50 M-14 N-4 99.00RM-2 1.00 M-15 N-5 99.70 RM-1 0.30 M-16 N-5 99.50 RM-1 0.50 M-17 N-699.70 RM-1 0.30 M-18 N-6 99.50 RM-1 0.50 M-19 N-7 99.70 RM-1 0.30 M-20N-7 99.50 RM-1 0.50 M-21 N-8 99.70 RM-1 0.30 M-22 N-8 99.50 RM-1 0.50M-23 N-9 99.70 RM-1 0.30 M-24 N-9 99.50 RM-1 0.50

Additionally comparable nematic LC mixtures CM-1 to CM-6 to theinvention are prepared from the nematic host mixtures N-1 listed aboveand photoalignment additives according to the prior art. Thecompositions are given in the following table.

Comparative c [%] of Photoalignment Mixture Host Host additive exampleMixture Mixture Compound c [%] CM-1 N-1 99.70 CRM-1 0.30 CM-2 N-1 99.50CRM-1 0.50 CM-3 N-1 99.00 CRM-1 1.00 CM-4 N-1 99.70 CRM-2 0.30 CM-5 N-199.50 CRM-2 0.50 CM-6 N-1 99.00 CRM-2 1.00

Cell Filling and Curing

Unless explicitly stated otherwise, the selected LC mixtures arecapillary filled using capillary action at room temp., annealed for 1 hat 100° C. and then irradiated at the same temperature with linearlypolarised UV light (35 mW/cm²) for the given time. The cells are thencooled to room temperature. Next, the alignment quality is studiedbetween crossed polarisers on a light box.

Curing Host mixture Compound time Example [%] [%] [s] Alignment M-1 N-199.70 RM-1 0.30 300 ++ M-2 N-1 99.50 RM-1 0.50 180 ++ M-3 N-1 99.00 RM-11.00 60 ++ M-6 N-1 99.70 RM-3 0.30 180 + M-7 N-1 99.50 RM-3 0.50 120 +M-8 N-1 99.00 RM-3 1.00 60 ++ M-9 N-2 99.50 RM-2 0.50 180 ++ M-10 N-299.00 RM-2 1.00 60 ++ M-11 N-3 99.50 RM-2 0.50 180 + M-12 N-3 99.00 RM-21.00 120 ++ M-13 N-4 99.50 RM-2 0.50 180 + M-14 N-4 99.00 RM-2 1.00 120++ M-15 N-5 99.70 RM-1 0.30 300 + M-16 N-5 99.50 RM-1 0.50 180 + CM-2N-1 99.50 CRM-1 0.50 120 + CM-3 N-1 99.00 CRM-1 1.00 120 ++ CM-5 N-199.50 CRM-2 0.50 120 ++ CM-6 N-1 99.00 CRM-2 1.00 60 ++ CM-7 N-1 100.00− − − − Alignment quality: (++) excellent, (+) good, (o) acceptable, (−)poor

At least good uniform planar alignment is achieved with all mixturesdespite from comparison mixture example CM-7. With mixtures comprisingCRM-1 is it not possible to reach the optimum dark state level at below1% concentration.

VHR Measurements

Unless explicitly stated otherwise, the selected LC mixtures arecapillary filled using capillary action at room temp., annealed for 1 hat 100° C. and then irradiated at the same temperature with linearlypolarised UV light (35 mW/cm2) from an Omnicure S2000 mercury lamp witha built in 320-500 nm filter either utilizing an additional 360 nm longpass filter (cuts off shorter wavelengths from 320-360 nm) or withoutsuch filter. The cells are then cooled to room temperature. Next, theVHR is studied using Toyo LCM-1 LC Material Characteristics MeasurementSystem. Unless described otherwise, the measurement of the VHR iscarried out as described in T. Jacob, U. Finkenzeller in “Merck LiquidCrystals—Physical Properties of Liquid Crystals”, 1997.

VHR measured at 100° C., 60 Hz and 1 V after curing without 360 nm cutoff filter

Host mixture Photoalignment compound VHR Example [%] [%] [%] M-1 N-199.70 RM-1 0.30 18.5 M-4 N-1 99.50 RM-2 0.50 23.5

VHR measured at 100° C., 60 Hz and 1 V after curing without 360 nm cutoff filter

Host mixture Photoalignment compound VHR Example [%] [%] [%] M-1 N-199.70 RM-1 0.30 92.6 M-4 N-1 99.50 RM-2 0.50 93.8

Host mixture Photoalignment compound Example [%] [%] Alignment CM-1 N-199.70 CRM-1 0.30 No alignment CM-2 N-1 99.50 CRM-1 0.50 No alignmentCM-3 N-1 99.00 CRM-1 1.00 No alignment CM-4 N-1 99.70 CRM-2 0.30 Noalignment CM-5 N-1 99.50 CRM-2 0.50 No alignment CM-6 N-1 99.00 CRM-21.00 No alignment

As can be seen from the above-given tables the VHR of test cells inaccordance with the present invention can be significantly improved byutilizing a 360 nm cut off filter while irradiating the test cells. Incomparison to the test cells according to the present invention, thetest cells utilizing the comparative mixtures CM-1 to CM-6 do not showany uniform alignment after curing utilizing a 360 nm cut off filter.

The invention claimed is:
 1. A compound of formula I,

wherein A¹¹ denotes a radical

where, in addition, one or more H atoms in these radical may each bereplaced by L, and/or one or more and/or one or more CH groups may eachbe replaced by N, A denotes, independently of one another, in eachoccurrence a) the group consisting of 1,4-phenylene and 1,3-phenylene,wherein, in addition, one or two CH groups may each be replaced by N andwherein, in addition, one or more H atoms may each be replaced by L, b)the group consisting of saturated, partially unsaturated or fullyunsaturated, and optionally substituted, polycyclic radicals having 5 to20 cyclic C atoms, one or more of which may, in addition, be replaced byheteroatoms, selected from the group consisting of

where, in addition, one or more H atoms in these radicals may each bereplaced by L, and/or one or more double bonds may each be replaced bysingle bonds, and/or one or more CH groups may each be replaced by N, c)group consisting of trans-1,4-cyclohexylene, 1,4-cyclohexenylene,wherein, in addition, one or more non-adjacent CH₂ groups may each bereplaced by —O— or —S— and wherein, in addition, one or more H atoms mayeach be replaced by F, or d) a group consisting oftetrahydropyran-2,5-diyl, 1,3-dioxane-2,5-diyl,tetrahydrofuran-2,5-diyl, cyclobutane-1,3-diyl, piperidine-1,4-diyl,thiophene-2,5-diyl and selenophene-2,5-diyl, each of which may also bemono- or polysubstituted by L, L on each occurrence, identically ordifferently, denotes —OH, —F, —Cl, —Br, —I, —CN, —NO₂, SF₅, —NCO, —NCS,—OCN, —SCN, —C(═O)N(R^(z))₂, —C(═O)R^(z), —N(R^(z))₂, optionallysubstituted silyl, optionally substituted aryl having 6 to 20 C atoms,or straight-chain or branched or cyclic alkyl, alkoxy, alkylcarbonyl,alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 25 Catoms, in which, in addition, one or more H atoms may each be replacedby F or Cl, or X²¹-S_(p) ²¹-R²¹, M denotes —O—, —S—, —CH₂—, —CHR^(z)— or—CR^(y)R^(z)—, and R^(y) and R^(z) each, independently of one another,denote H, CN, F or alkyl having 1-12 C atoms, wherein, in addition, oneor more H atoms may each be replaced by F, Y¹¹ and Y¹² each,independently of one another, denote H, F, phenyl or optionallyfluorinated alkyl having 1-12 C atoms, Z denotes, independently of eachother, in each occurrence, a single bond, —COO—, —OCO—, —O—CO—O—,—OCH₂—, —CH₂O—, —OCF₂—, —CF₂O—, —(CH₂)_(n)—, —CF₂CF₂—, —CH═CH—, —CF═CF—,—CH═CH—COO—, —OCO—CH═CH—, —CO—S—, —S—CO—, —CS—S—, —S—CS—, —S—CSS— or—C≡C—, n denotes an integer between 2 and 8, o and p denote each andindependently 0, 1 or 2, X¹¹ and X²¹ denote independently from oneanother, in each occurrence a single bond, —CO—O—, —O—CO—, —O—COO—, —O—,—CH═CH—, —C≡C—, —CF₂—O—, —O—CF₂—, —CF₂—CF₂—, —CH₂—O—, —O—CH₂—, —CO—S—,—S—CO—, —CS—S—, —S—CS—, —S—CSS— or —S—, Sp¹¹ and Sp²¹ denote each andindependently, in each occurrence a single bond or a spacer groupcomprising 1 to 20 C atoms, wherein one or more non-adjacent andnon-terminal CH₂ groups may also each be replaced by —O—, —S—, —NH—,—N(CH₃)—, —CO—, —O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O—, —CF₂—, —CF₂O—,—OCF₂— —C(OH)—, —CH(alkyl)-, —CH(alkenyl)-,-CH(alkoxyl)-,—CH(oxaalkyl)-, —CH═CH— or C≡C—, however in such a way that no twoO-atoms are adjacent to one another and no two groups selected from—O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O— and —CH═CH— are adjacent to eachother, R¹¹ denotes P, R²¹ denotes P, or halogen, CN, optionallyfluorinated alkyl or alkenyl with up to 15 C atoms in which one or morenon adjacent CH₂-groups may each be replaced by —O—, —S—, —CO—, —C(O)O—,—O—C(O)—, O—C(O)—O—, and P each and independently from another in eachoccurrence a polymerizable group.
 2. The compound according to claim 1,wherein the compound is selected from compounds of -sub-formulae I-1 toI-9,

wherein R¹¹, R²¹, A¹¹, X¹¹, X¹², Y¹¹, Y¹², Sp¹¹, and Sp¹² have one ofthe meanings as given above in claim 1, A¹² to A²³ have one of themeanings for A as given in claim 1, and Z¹¹ to Z²² have one of themeanings for Z as given above in claim
 1. 3. The compound according toclaim 1, wherein the compound is selected from compounds sub-formulaeI-1a-1, I-2a-1, and I-3a-1,

wherein R¹¹, R²¹, X¹¹, X²¹, Sp¹¹, and Sp²¹ have one of the meanings asgiven above in claim 1, Z¹¹ and Z²¹ have one of the meanings for Z asgiven above in claim 1 and the group

is each and independently

or denotes

furthermore

wherein L is F, Cl, CH₃, OCH₃ and COCH₃ or alkylene having 1 to 6 Catoms, or X²¹-Sp²¹-R²¹.
 4. The compound according to claim 1, whereinsaid compound is selected from compounds of sub formulae I-3a-1a,I-3a-1b, and I-3a-1c,

wherein R¹¹, R²¹, X²¹, and Sp²¹ have one of the meanings as given abovein claim 1, Z²¹ has one of the meanings for Z as given above under claim1, r, s, t and q denote each and independently from another an integerfrom 1 to 8, Y denotes each and independently from each other methyl orH, and the group

is each and independently

or denotes

furthermore

wherein L is F, Cl, CH₃, OCH₃ and COCH₃ or alkylene having 1 to 6 Catoms, or X²¹-Sp²¹-R²¹.
 5. The compound according to claim 1, whereinsaid compound is selected from compounds of sub-formulae I-3-1a-1 toI-3-1a-8,

wherein Sp²¹ has one of the meanings as given above in formula I, and Ldenotes F, Cl, OCH₃ and COCH₃ or alkylene having 1 to 6 C atoms.
 6. Thecompound according to claim 1, wherein said compound is selected fromcompounds of sub-formulae I-3-1b-1 to I-3-1b-4,

wherein Sp²¹ has one of the meanings as given above in formula I, and Ldenotes F, Cl, OCH₃ and COCH₃ or alkylene having 1 to 6 C atoms.
 7. Amethod of photoaligning a liquid crystal mixture comprising irradiatinga liquid crystal mixture with linearly polarized light wherein saidliquid crystal mixture contains one or more compounds of formula Iaccording to claim
 1. 8. A liquid crystal mixture, comprising: acomponent A) comprising one or more compounds of formula I according toclaim 1, and a liquid-crystalline component B), comprising one or moremesogenic or liquid-crystalline compounds.
 9. The liquid crystal mixtureaccording to claim 8, wherein the total concentration of compounds offormula I in the mixture is in the range of from 0.01 to 10% by weight.10. The liquid crystal mixture according to claim 8, further comprisinga polymerizable component C) comprising one or more polymerizablemesogenic or polymerizable isotropic compounds.
 11. The liquid crystalmixture according to claim 10, wherein the concentration ofpolymerizable mesogenic or polymerizable isotropic compounds is in therange of from 0.01 to 10% by weight.
 12. The liquid crystal mixtureaccording to claim 10, wherein said mixture contains one or morepolymerizable compounds of formula PP^(a)-(Sp^(a))_(s1)-A²-(Z^(a)-A¹)_(n2)-(Sp^(b))_(s2)—Pb  P whereinP^(a), P^(b) each, independently of one another, denote a polymerizablegroup, Sp^(a), Sp^(b) on each occurrence, identically or differently,denote a spacer group, s1, s2 each, independently of one another, are 0or 1, A¹, A² each, independently of one another, denote a radicalselected from the following groups: a) the group consisting oftrans-1,4-cyclohexylene, 1,4-cyclohexenylene and 4,4’-bicyclohexylene,wherein, in addition, one or more non-adjacent CH₂ groups may each bereplaced by —O—or —S— and wherein, in addition, one or more H atoms mayeach be replaced by F, b) the group consisting of 1,4-phenylene and1,3-phenylene, wherein, in addition, one or two CH groups may each bereplaced by N and wherein, in addition, one or more H atoms may each bereplaced by L, c) the group consisting of tetrahydropyran-2,5-diyl,1,3-dioxane-2,5-diyl, tetrahydrofuran-2,5-diyl, cyclobutane-1,3-diyl,piperidine-1,4-diyl, thiophene-2,5-diyl and selenophene-2,5-diyl, eachof which may also be mono- or polysubstituted by L, d) the groupconsisting of saturated, partially unsaturated or fully unsaturated, andoptionally substituted, polycyclic radicals having 5 to 20 cyclic Catoms, one or more of which may, in addition, be replaced byheteroatoms, that are selected from:

where, in addition, one or more H atoms in these radicals may bereplaced by L, and/or one or more double bonds may each be replaced bysingle bonds, and/or one or more CH groups may each be replaced by N, n2is 0,1,2 or 3, Z¹ in each case, independently of one another, denotes—CO—O—, —O—CO—, —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂—, —(CH₂)_(n)— where n is2, 3 or 4, —O—, —CO—, —C(R⁰R⁰⁰)—, —CH₂CF₂—, —CF₂CF₂— or a single bond, Lon each occurrence, identically or differently, denotes F, Cl, CN, SCN,SF₅ or straight-chain or branched, in each case optionally fluorinated,alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy oralkoxycarbonyloxy having up to 12 C atoms, R⁰, R⁰⁰ each, independentlyof one another, denote H, F or straight-chain or branched alkyl having 1to 12 C atoms, wherein, in addition, one or more H atoms may each bereplaced by F, M denotes —O—, —S—, —CH₂—, —CHY¹— or —CY¹Y²—, and Y¹ andY² each, independently of one another, have one of the meaningsindicated above for R⁰ or denote Cl or CN.
 13. The liquid crystalmixture according to claim 8, wherein component B has negativedielectric anisotropy.
 14. The liquid crystal mixture according to claim13, wherein component B comprises one or more compounds selected fromformulae CY and PY:

wherein a is 1 or 2, b is 0 or 1,

denotes

R¹ and R² each, independently of one another, denote alkyl having 1 to12 C atoms, where, in addition, one or two non-adjacent CH₂ groups mayeach be replaced by —O—, —CH═CH—, —CO—, —O—CO— or —CO—O—in such a waythat O atoms are not linked directly to one another, Z^(X) denotes—CH═CH—, —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂—, —O—, —CH₂—, —CH₂CH₂— or asingle bond, and L¹⁻⁴ each, independently of one another, denote F, Cl,OCF₃, CF₃, CH₃, CH₂F, CHF₂.
 15. The liquid crystal mixture according toclaim 8, wherein component B has positive dielectric anisotropy.
 16. Theliquid crystal mixture according to claim 15, wherein component Bcomprises one or more compounds selected from compounds of formulae IIand III,

wherein R²⁰ each, identically or differently, denote a halogenated orunsubstituted alkyl or alkoxy radical having 1 to 15 C atoms, where, inaddition, one or more CH₂ groups in these radicals may each be replaced,independently of one another, by —C≡C—, —CF₂O—, —CH═CH—,

—O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directlyto one another, X²⁰ each, identically or differently, denote F, Cl, CN,SF₅, SCN, NCS, a halogenated alkyl radical, a halogenated alkenylradical, a halogenated alkoxy radical or a halogenated alkenyloxyradical, each having up to 6 C atoms, and Y²⁰⁻²⁴ each, identically ordifferently, denote H or F, W denotes H or methyl, and

each, identically or differently, denote


17. The liquid crystal mixture according to claim 15, wherein saidmixture comprises one or more compounds selected from compounds offormulae XI and XII

wherein R²⁰ denotes a halogenated or unsubstituted alkyl or alkoxyradical having 1 to 15 C atoms, where, in addition, one or more CH₂groups in these radicals may each be replaced, independently of oneanother, by —C≡C—, —CF₂O—, —CH═CH—,

—O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directlyto one another, X²⁰ each, identically or differently, denote F, Cl, CN,SF₅, SCN, NCS, a halogenated alkyl radical, a halogenated alkenylradical, a halogenated alkoxy radical or a halogenated alkenyloxyradical, each having up to 6 C atoms, Y²⁰⁻²³ each identically ordifferently, denote H or F, W denotes H or methyl, and

each, independently of one another, denote

and

denotes


18. The liquid crystal mixture according to claim 8, wherein component Bcomprises one or more compounds of formula ZK:

in which the individual radicals have the following meanings:

denotes

denotes

R³ and R⁴ each, independently of one another, denote alkyl having 1 to12 C atoms, in which, in addition, one or two non-adjacent CH₂ groupsmay be replaced by —O—, —CH═CH—, —CO—, —O—CO— or —CO—O— in such a waythat O atoms are not linked directly to one another, and Z^(y) denotes—CH₂CH₂—, —CH═CH—, —CF₂O—, —OCF₂—, —CH₂O—, —OCH₂—, —CO—O—, —O—CO—,-C₂F₄—, —CF═CF—, —CH═CH—CH₂O— or a single bond.
 19. The liquid crystalmixture according to claim 8, wherein component B comprises one or morecompounds of the following formula

wherein the propyl, butyl and pentyl groups are straight-chain groups.20. The liquid crystal mixture according to claim 8, wherein component Bcomprises one or more compounds selected from the formulae B1 to B3:

in which alkyl and alkyl* each, independently of one another, denote astraight-chain alkyl radical having 1-6 C atoms, and alkenyl andalkenyl* each, independently of one another, denote a straight-chainalkenyl radical having 2-6 C atoms.
 21. The liquid crystal mixtureaccording to claim 8, wherein component B comprises one or morecompounds selected from the following formulae:

in which alkyl* denotes an alkyl radical having 1-6 C atoms.
 22. Amethod of photoaligning the liquid crystal mixture according to claim 8comprising irradiating the liquid crystal mixture with linearlypolarized light.
 23. A process the fabrication of a liquid crystaldisplay, comprising: providing a first substrate which includes a pixelelectrode and a common electrode for generating an electric fieldsubstantially parallel to a surface of the first substrate in the pixelregion; providing a second substrate, the second substrate beingdisposed opposite to the first substrate; interposing a liquid crystalmixture according to claim 8; irradiating the liquid crystal mixturewith linearly polarized light causing photoalignment of the liquidcrystal; and curing the polymerizable compounds of the liquid crystalmixture by irradiation with ultraviolet light or visible light having awavelength of 450 nm or below.
 24. The process according to claim 23,wherein the linearly polarized light is ultraviolet light or visiblelight having a wavelength of 450 nm or below.
 25. A display obtainableby a process according to claim
 23. 26. The display according to claim25, wherein component B is homogeneously aligned without the applicationof an electric field.
 27. The display according to claim 25, wherein thedisplay is an IPS or FFS display.